Fair point on the nano-tech. The alternative I had is a large number of reconfigureable blocks which can be arranged into a number of shapes, akin to Replicator blocks from the Stargate series. With just a slight change to frequencies and signals it can rearrange the blocks into a different shape. I mean Necron lords have mechanical scarab swarms which cover them and reduce ranged damage so I was thinking of using the same idea but not giving the ranged resistance and focusing it on rebuilding their weapons on a whim.

With regards to added weapons I was thinking of keeping the current tau arsenal. I mean with the ability of switching in a few seconds from hammering them at a distance and softening them up with two arm mounted missile systems, closing in to pin down with double burst cannons before going up close for the kill with flamers and fusion blasters, not sure if they need much more! I love the EMP idea and spotted something in the Tau Character Guide for RT which unleashes a radial effect disrupting tech. I was tempted to keep it as well as integrating a fine mesh to channel counter EMP shots and mitigate the electrical discharge.

To stop suit grappling, this is why it has a jump pack with the standard upgrade of Vectored Retro Thrusters (Half action to freely disengage from melee). Alternatively though if you do grab onto it, it can just throw itself up into the air with a jump and see how long you can hold on for.

From an engineering standpoint, the big problem I see with all this is power budget. This looks like Riptide-plus levels of power usage (necron forcefields, weapons and wargear are very energy hungry).

New grenade munitions, the incorporation of Imperial technology, advanced metallurgical adaptations of adamantium? That's cool. But adamantium is what armours the (slow, lumbering but powerful) Terminators. Vectored Retrothrusters on something with that much mass won't provide much maneuverability unless they are very, very powerful- then you're looking at them doubling as weapon systems (a la Iron Man repulsor-as-weapon-and-propulsion) and chewing up your power budget again.

Actually, the Iron Man movie makes a good comparison here. Compare the Iron Man armour to the Warmonger armour- there Warmonger had much heavier armour and similar straight-line flight ability (thanks to large, powerful rockets) but wouldn't have been able to match Ironman's mobility. You're trying to uparmour Ironman without losing mobility.

But, if this is a rogue sept with dramatically improved power plants, microthrusters, energy storage and distribution systems, and metallurgical techniques, then go for it. I also recommend a hammerhead with an ion cannon with three modes of fire (wide area blast, high damage two-shot, and standard but with assault-cannon rate of fire), hardened armour and falcon gravtank mobility, or gun drones equipped with light ion cannon or plasma rifles. Fire warriors with jump gear and fusion guns. That's the sort of thing that would happen with that kind of tech leap.

Pretty much that this is a fully rogue sect. Their main idea is that any technology is worth considering. Ethereals tend to believe that Tau technology is always superior and that some Xenos tech is seldom worth their time. This is wrong and an oversight and this sect see that and acknowledge that sometimes the enemy might be on to something. Additionally they acquire gear differently. While the Tau discuss and go with diplomacy, this group don't go with that. If they see something they like, they take it and have no objection with testing any experimental methods on their own units and there are even rumours of genetic alteration techniques acquired from captured bio-magos.

Their radical nature is also a plot angle I was looking to go with to bring the main empire into it. Their methods are damaging the reputation of Tau with other races and their methods are crude and ill-fitting that of the greater good. A deal with the devil on the cards. If the rogue sect wins then it would mean a dramatically reinforced and overhauled Tau force. Imagine some of the above being the standard on the battlefield, the Imperium would be terrified. This is why they would be keen to see this stopped. But also look at the reverse, the KT could choose to leave the rogue sect intact as every action they perform keeps the Tau occupied on this front to deal with them and in time could force a civil war which causes them to be destroyed by infighting. It's two very strong ideas and whichever wins out could shift the power balance. The KT are stuck in the middle as this infighting is a threat to Imperial resources in the area.

So with that in mind the issues you raised are something to consider.

First off I found a fantastic sketch done on a blog which could look suitably imposing and fit the roll although other suggestions are welcome.
http://battlesuits.blogspot.co.uk/2011_08_01_archive.html
(Second and third images)

I was thinking for power requirements either a scaled down nova reactor (which we know has issues anyway) or doing a GW and pulling an idea out of thin air just to one up to say that they have found some unknown race which has better power facilities something like using antimatter or ZPMs, whatever it is. Either way there are consequences to using this, one such is don't overload the **** thing or it'll make a nice crater.

Otherwise weight is an issue. I've made it an adamantium/iridium alloy rather than pure adamantium but yes weight is a factor. I was thinking to that end of incorporating lesser grav technology as part of the thrusters. Tau, Eldar and Imperium do have the technology to make things hover so use that to try and offset the weight of the thing enough to let the engines kick in. It's not as mobile though as a standard XV8 Tau suit by any account and its flyer quality will suffer as a result but it can still get some serious movement. I might look into the Warmonger suit though for an idea of how it operates and how to use this as a comparison, cheers for that!

I love the last few little bits though, I was thinking railguns with a semi-auto mode...two shots at slightly lower power. Standard infantry gear a little better somehow, might see if I can come up with something to give the Fire Warrior a little more bite. I do also enjoy the idea of adding some heavier weapons to drones. They already have rail rifle and pulse carbine as well as long burst cannons on the remora so add a few plasma/fusion or possibly a cyclic ion blaster and you have something which hurts.