Here, I proudly present a system I designed for one of my players who wanted to know how many percent of his Explorator would be mechanical and how many biological. This is what I came up with:

The Path of the the Omnissiah
All good things come in threes: Insanity, Corruption and Mechanization
Mechanization Points (MP) represent how far a character’s body and mind have become mechanized. This characteristic starts at a value of 0 and increases whenever one comes closer to being a machine. The Omnissian Track works similar to the Insanity and Corruption tracks. By accumulating MP, a character advances on the track.
However, in contrast to IP and CP, the path of the machine is constant and predictable, it is the way to the divine logic of the Machine God rather than the incomprehensible process of corruption in flesh and mind.
This system is designed primarily for the Explorator PCs. In order to integrate the MP system into the rules as written, it is advisable to remove the talents “The Flesh is Weak” from the Explorator’s Career Advance Scheme.

Acquiring Mechanization Points
There are two common ways of acquiring MP: The first is buying tech-related talents. The following talents are considered to be tech-related:
· All talents with the prerequisite trait “Mechanicus Implants”
· Autosanguine
· Binary Chatter
· Conceiled Cavity
· Electro Graft Use
· Enhanced Bionic Frame
· Logis Implant
· Prosanguine
How many MP each of these talents grant depends on their XP cost in the Explorator’s advance scheme: Talents with an XP cost of 200 grant 1 MP, while talents with an XP cost of 500 grant 3 MP.

The second common way of acquiring MP is attaching cybernetics to one’s body. They are categorized as follows:

Enormous:
The complex Mechanicus Implants are a category of their own: a character with this trait acquires 9 MP.

Major:
This category comprises large cybernetics (a whole Respiratory System, all kinds of Mechadendrites, Bionic Limbs or anything similar in size) as well as implants that significantly alter the brain structure (MIU, Cortex Implants or the like).
Each major cybernetic grants 5 MP to the character it is attached to.

Minor:
This includes technically advanced smaller cybernetics with active functions (Scribe tines, MIU Weapon Interface, all kinds of artificial senses, Bionic Heart, etc) and minor neural augmetics (Locator Matrix, Memorance and Volitor Implants and so on).
A character acquires 3 MP for every attached minor cybernetic.

Trivial:
Low level tech augmetics, either very small (Vox Implant) or only providing passive features (Skin Implants, Cranial Armour) all belong into this category.
Each trivial cybernetic grants 1 MP to the character it is attached to.

Degrees of Mechanization
The Omnissian Track is divided into six Degrees of Mechanization as described below. Whenever a character has accumulated enough MP, he automatically acquires the next degree and is then subject to the rules corresponding to it.

0-9: Of flesh and blood
The character possesses either few and unremarkable cybernetics or none at all.
These will not attract any special attention under most circumstances or have any effects other than those explained in the rulebook.

10-29: Augmented
First marks of not being entirely natural become obvious. Beholders might wonder whether the character adopted the bionics deliberately or was forced to do so because he needs them in his everyday work and life.
Struggling Body: The character’s flesh is not yet accostumed to the various pieces of metal it houses. Whenever suffering hard physical strain, an Ordinary (+10) Toughness test must be passed. Failure indicates an inflammation has occurred and a single random cybernetic may not be used until the inflammation is cured.

30-49: Mechanized
The character’s body is fitted with an increasing number of strange devices. More often than before, he acts like a machine.
He gains the Machine (1) trait and constantly reduces his Fellowship by 1d5*.
Mental Conflict: As the unsystematic thoughts of his human mind struggle with the logical calculations of his circuitry, the character suffers 1d10 IP. Nevertheless, his body has adapted to the implants and is no longer subject to the inflammation rule.

50-69: Man & Machine
Having overcome the weakness and doubts that plague lesser servants of the Omnissiah, the character follows the belief in the machine’s superiority with zeal and certainty.
He gains the Machine (2) trait, and constantly reduces his Fellowship by another 1d5*.
Challenging Patient: Healing the character with the Medicae skill becomes hard (-20) and can only restore his health to a maximum number of wounds equal to his TB because large parts of his weak flesh are already substituted by pure metal. Further healing requires correlative Tech-Use tests. At the GM's discretion, surgeons treating the character might significantly hurt themselves when accidently cutting through power cables etc.

70-89: Forged of Iron
The character frees his body more and more from the frailty of natural tissue.
He gains the Machine (3) trait, and constantly reduces his Fellowship by another 1d5*.
Manufactured, not grown: The character no longer heals naturally. He can only be healed through Tech-Use tests (base difficulty of Challenging (+0)) equivalent to Medicae skill tests. These tests become very hard (-30) whenever there are no appropriate spare parts at hand.

90-99: Avatar of the Machine God
Well-nigh nothing is left of the human being this machine once was.
It gains the Machine (4) trait, and constantly reduces its Fellowship by another 1d5*.
Mechanical Purity: The machine is free from emotions and (nearly) all human needs (e.g. sleep), but also has to maintain his augmetics carefully, i. e. it must spend at least one hour each day on performing respective rites. These are represented by a Routine (+20) Trade (Technomat) test. Failure causes one level of fatigue which will last until the next successful maintenance test. The Manufactured, not grown rules apply as well.

*The Fellowship characteristic may never fall below 01 through this.

Optional Rule: This is an idea that I personally found interesting but did not work out in detail: At the GM's discretion, certain talents or implants may only be acquired if a character possesses a sufficient Degree of Mechanization, e.g. "Enhanced Bionic Frame" might require the character to have a Mechanization degree of Man & Machine (at least)

Interesting idea, I will bounce it to my players and see what they think of it. Especially the Tech Priest

I just finished the last entry on the Track:

100+: Machine Soul
Finally, along with the digitalization of more and more of his thoughts, the character’s very soul has been transcribed into another complex programm running on his cogitator circuitry, ready to be uploaded on the Machine Altars of the Adeptus Mechanicus.
The PC looses another 1d5 Fel (may not fall below 01 through this), Mechanical Purity and Manufactured, not grown still apply to his body.
Anima Codica: With a successful Willpower Test as a Full Action, the PC may upload his soul onto any machine capable of housing a machine or weapon spirit. The difficulty of the test is based on the machine’s complexity, ranging from Easy (+30) for simple devices such as a lasgun to Very Hard (-30) for machines as complex as starship components. If the GM deems the spirit of the targeted machine sophisticated enough, the test becomes an Opposed Willpower Test.
Example: In search of an STC, Magos Torian and his companions are chasing scavengers in the burnt wastelands of Zayth. Fortunately, the Magos finds an old battle tank. With a Hard (-20) Willpower Test, Torian uploads his soul through a data port into the cogitator core.

The exact effects of a success by the PC are various and up to the GM. Generally, the machine will only do what the character wants it to do. Only under adverse conditions, the PC should need to make tests for operating the machine. Additionally, he may substitute any appropriate Test with an Intelligence Test. A weapon housing the soul may be counted as being of best quality and refuse to be triggered normally, controlled only by the strange spirit.
Example: Because the tank is chasing the scavengers in rough terrain, the GM demands an Ordinary (+10) Drive Skill Test. As the tank now acts as Torian’s body, the Magos does not need to possess the skill and instead makes an Ordinary Intelligence Test. Firing the tank’s guns will still require a Ballistic Skill Test, but the PC counts as having all corresponding types of Weapon Training. Furthermore, while uploaded, Torian is not capable of hearing anything because the machine only possesses visual sensors etc.

The soul programm in the body is deleted as soon as it is transmitted to a machine, so that there can only be one soul at all times. This also means that the character’s normal body is then immobile like a statue, unable to take any actions as long as it does not house the soul. Transmitting the soul programm back to the body can be done with another Ordinary (+10) Willpower Test as a Full Action.

Feel free to comment and suggest improvements.

coming mainly from DH here:

as I see this most similar feelowship loss effects specify it can't fall below 5 fellowship (radicals for example I think features some effects) maybe you want do adopt this...

if using this rules for tech-priests maybe you want to allow them natural fellowship advances... cutting them even more in fellowship is more or less denying any fellowship based stuff for them

I think some negative effects should wear of after a while (not yet accustomed to implants? heck there are people out there living for several hundreds of years and they don't get accustomed to bio implants because they don't add more?)

An option you might want to consider instead of the general fellowship reductions, is to give a penalty to fellowship for interactions with those who are not part of the cult of the machine. Also, uploading would probibly only work on a vehicle that already possesses a Machine Spirit.

Sirion said:

Ok, the Fellowship limit could be increased to 5. Admittedly, in my own campaign, it wil not make much of a difference, because the Explorators' Fellowship probably won't decrease that much.

DH Techpriest should definitely get to buy natural fellowship advances when using this system. I suggest to make only the simple and intermediate Advance available for 1000/2500xp. However I think this system would generally have to be redesigned in large parts because of the general difficulty of getting (finding, paying and successfully implanting) cybernetics in DH. The relation between xp cost and machine points also won't really work out because RT PCs pay more for their talents. As I stated, this is designed for Explorators. That also answers the accustomization issue. I intended this for a player who wants to be a machine. Before becoming one, however, I want him to go through some suffering.

Another optional rule: When communicating with members of the Machine Cult, a character automatically gets a bonus to all Fellowship-related tests. This bonus is equal to half the number of Mechanization Points he has.

Or: When communicating with members of the Machine Cult, a character automatically gets a bonus to all Fellowship-related tests. This bonus depends on his Degree of Mechanization: Mechanized +10, Man & Machine +20, etc. up to Machine Soul +50.