>>>EDIT: Added backstory and retouched image!<<<
For those who remember this piece of mine: [link]
and left cool story ideas about the origins of such a "heretical" IG design, thank you! I've been considering different plots and the whole Tau engineering collaboration + Gue'vesa auxillary idea seemed the most plausible and exciting for me.
Here's an updated story on its origins:
The Phobos Pattern was originally designed by an eccentric, albeit well-meaning techpriest on a forgeworld along the dark fringes of Imperium space. It was built in memory of his son, who died on an icy moon while serving as a Imperial Guard conscript in some forgotten campaign against Tyranids.
His labour of love, the Phobos Pattern, a semi autonomous exo-suit, was designed for normal human proportions, and for deployment amongst the Imperial Guard. The suit was not intended to replace or even come close to an Astartes armour, but act as a 'force multiplier' to bolster IG ranks and to allow once disabled soldiers to fight as equals alongside their own. Once complete, the Phobos MK1 plans were presented to the Imperium, and deemed absolutely heretical. As a result, his Forgeworld was to be swept by Space Marine kill teams in a purge mission. The Older brother sent to kill the younger brother as ordered by their Father.
The small Astartes force that was sent to wipe them out realised the visionary aspect of the project during the mission briefing itself, but continued their mission without question for fear of being labelled traitors.
The IG test-pilot force that comprised of young and old, able-bodied and paraplegic, all suited up in Phobos Pattern armour and fought back bravely to preserve their project; as well as to prove their undying love for the Imperium's future.
Eventually, the Astartes force was reduced to the last Marine, a Sargeant who called down an orbital nuclear bombardment when the mission was deemed a failure.
In his final moments he looks on as a shuttle escapes the facility and into the warp, and with it, the construction template for the Phobos Pattern armour. That was his only act of defiance to the Emperor in his lifetime as a Space Marine, one that he hoped would help pave the way to a brighter future for the Imperium.
The shuttle emerged from the warp years later, and found itself in Tau space. The Tau, learning of its origins and potential, openly embraced the Phobos Pattern prototype and began additional R&D work to implement it into their Gue'vesa/Human Auxillary force.
In this scenario, the Tau combat systems research/construction facility that manufactures the Phobos Pattern armour itself, also maintains an actual Tyranid hatchery on location to be used in live combat trials. As such, they operate on a remote population-free moon due to security concerns.
A major security breach later, and the only surviving Tau (the facility commandant) and his trusted aide and Gue'vesa hold off the escaped Tyranid specimens till a rapid response lockdown crew arrives. The facility's personnel sacrificed themselves to buy him time to download the Pattern construction plan and hotfoot it to the extraction point, and he is clearly determined to see the mission(and their valiant sacrifice) through. The Tau force evacuating them are a special stealth-only anti-'Nid detachment sporting customised gear: XV25 suits and Super-Remora drones as well as a Longbow Heavy Sniper drone to neutralise hardened specimens.
"Bear with the pain, commandant! Hammerhead is inbound. The plans must survive for the greater good!"