So I really disliked the psychic powers in the beta, and was only okay with the powers in Only War. The previous systems had some cool aspects, but I honestly felt like psychic powers have just been incrementally doing away with a lot of the flavor that DH 1 had. I can't think of anyone who really had a problem with the plethora of minor powers in DH1, and the primary complaint was how massively unbalanced the powers were. I obviously don't know what direction the devs want to go with psychic powers, but I'd like to throw in my own ideas.
Discipline Themes
Psychic powers represent literal raw chaos being shapes into the desires of man. The way this chaos is shaped is based on the desires of man. Man desires pain and destruction (Khorne), man desires mastery of life (Nurgle), man desires control and knowledge (tzeench), and man desires experiences and success (Slaanesh). Every time that a psychic power is invoked, it does so through tribute to one chaos god or the other. The needs that man shapes the warp for are the same needs that feed the chaos gods. I don't want the psychic powers to just feel like a risky magic system. I'd really like to see them reflect these themes at a deeper level than "melta gun that may cause a daemon to show up".
Here are my proposed themes for each of the Disciplines:
Biomancy: This represents human desire for mastery over life, and mastery of their own body.
Divination: This represents the human desire for knowledge and knowing what is to come.
Pyromancy: Pyromancy is both destruction AND creation. Fire or raw energy is the universal human tool used for both, and powers almost all technology at some basic level.
Telepathy: Telepathy is the desire for closeness to others, and secrets. This differs from the knowledge of Divination, as secrets are those things that another consciousness has deemed worthy of protection whereas knowledge is the raw state of facts.
Telekinesis: Control. This is mans desire to project himself into the world, to control his surroundings through will AND machine.
Power Level and Progression
This has seen multiple iterations. OW had an interesting idea for minor manifestations, but the lack of guidelines made it kind of hard to determine how to make them work (can I use biomancy as a heartbeat lie detector? Can I use pyromancy to light a spark inside of someone's ammo?). Pushing in the beta was also a mess. In general, the major theme for the game has been having minor low risk powers, mid-risk powers, and high risk or guaranteed risk powers.
There has also been a theme for psychic powers of vertical progression, with many powers being improved versions of others. Some of the disciplines have horizontal progression that allows a broad array of ideas and abilities to be addressed (telepathy) and some just focus on one thing with a lot of vertical progression (pyromancy).
I would propose the following for psychic powers. First, I would like to see each psychic power within the discipline addressing a unique idea or use, full horizontal progression. Second, I would like to see each power divided up into 3 versions: minor, major, and pushed. Minor powers would represent very fleeting or small transient bonuses that would be usable in a broad array of situations. Major would be more powerful uses of the power, and would scale with Psy level. Major uses would have more specific guidelines for use. The pushed version of a power would be very strong, and would also scale with psy level. Pushed uses of a power would likely require some sort of sacrifice to be used (corruption, insanity, temporary or permanent characteristic loss?). I don't want to comment too much on how these would interact with perils of the warp, as that will have to be based more on the system that is introduced.
Characteristics
I have a quick resolution for the problem with some psychic disciplines using characteristics that are more or less expensive to most psykers: allow characters to choose a single discipline and switch the xp costs of the characteristic associated with that discipline with the xp costs of one of their other characteristics.
The powers themselves!
Here we go! I'll just put one discipline up for now, and try to get more up as I go.
Biomancy
Perfect the Flesh
Minor: the character may gain a +10 bonus to a roll involving strength, agility, or toughness by perfecting his existing bodily processes at the precise moment. This can be used successfully once per scene.
Major: The character may add his Psy Level to the bonus of Strength, Agility, or Toughness for the remainder of the scene. This power can only affect a single trait at a time.
Pushed: The character may add his Psy Level to Strength, Toughess, AND Agility for the remainder of the scene.
Reshape the Flesh
Minor: The character may gain +10 to a roll involving his appearance, whether that involves disguising himself, influencing someone with his appearance, or other uses. This may not be used to copy features of another character. This lasts for one scene.
Major: The character may gain one Trait from the list below (I'll have to see what the traits are before I could make a list). The player may keep this trait for a number of rounds equal to his Psy Rating.
Pushed: The character may choose up to three Traits from the list. The player may keep these traits for a number of rounds equal to his psy rating.
Corrupt the Flesh
Minor: The character may mark a target human such that they are now detectable by psyniscience due to the mild corruption of their flesh. The target also exudes an air of unease that causes them to gain -10 to social rolls meant to make a positive impression. This power lasts for 1 day and can be used on one target at a time.
Major: This power causes a target's body to warp and deform. Choose strength, agility, or toughness and reduce its bonus by 1 for every 2 Psy Rating. If this reduces the bonus to 0 or less, the target suffers damage to the body equal to the Psy Rating, ignoring toughness and armour.
Pushed: The same as above but reducing all three characteristics. Deal damage for each characteristic bonus reduced to zero or below.
Reflect the Flesh
Minor: The character may copy the appearance of another human. The character keeps all of her characteristics and traits. This power lasts for one scene.
Major: The character may copy the appearance and body of another human (non-space marine). The character may copy the strength, agility, and toughness characteristics of the target character but not traits. Characteristics increased in this manner may increase a maximum of 10 points for every two levels of Psy Rating. This power lasts for a number of rounds equal to psy rating if characteristics are copied, or one scene otherwise.
Pushed: The character may copy the body of any target of size one or less greater than herself. The character may gain the strength, agility, toughness and traits of the target. Characteristics increased in this manner may increase a maximum of 10 points for every two levels of Psy Rating. If those are copied, this power lasts a number of rounds equal to 1/2 psy level, otherwise it lasts for one scene.
Destroy the Flesh
Minor: The character is able to stimulate the nerves to inflict a brief moment of excruciating pain on a target. This does not inflict wounds but can be used to gain a +20 bonus to intimidate. The target must make a willpower check or suffer -10 to his next action.
Major: This would be your basic psychic attack. Have it be te lightning. 1d10 + Psy Rating, +1 Pen per 2 Psy Rating, Tearing.
Pushed: This attack can target a number of characters equal to Psy Rating divided by 2.
Mend the Flesh
Minor: The character can diagnose the number and nature of a target's wounds, as well as any poisons or diseases. Gain +20 to any attempt to treat the target or for aiding treatment.
Major: The character can heal damage based on his Psy Rating. I'd have to see the wound system to know what values to give this.
Pushed: The character may may revive a dead target that has less wounds over his death total than the characters Psy Rating. The target must burn a Fate Point or will die again at the end of the scene.
Control the Flesh
Minor: The character may cause a single part (head, body, limb) of a target to spasm. The target takes a -10 for one round to any test made using that body part.
Major: The character may choose a single limb of the target. The target may not move that body part for a number of rounds equal to Psy Rating divided by 2. Tests made that require that body part for assistance are at -20.
Pushed: Make an opposed willpower test with the target. On a success the character may cause a target to not be able to move her body at all for a number of rounds equal to Psy Rating divided by 2. On a failure the target may choose 2 limbs that cannot be moved for a number of turns turns equal to Psy Rating divided by 2.
Know the Flesh
Minor: The character is able to detect all living things within a 10m radius. The character knows the exact location of all living things within 30 yards.
Major: The character chooses a target and reduces the damage number needed to roll a Righteous Fury against the target by 1 for every 2 Psy Rating.
Pushed: The characters next hit against a target will be a Righteous Fury.
So these are the basics. Not all of these powers are perfect but I think they cover a broad depth and breadth of actions. I tried to make the minor actions mostly good for no combat utility, the major actions all useful in at least combat, and the pushed actions all being very powerful. The major and pushed actions all also scale with Psy rating. I'm interested to see what people think of this approach, and if there's some positive interest Ill write up the other disciplines and send it to FFG.