[@PrivateVentures] It's coming along, but there's still balancing issues and some gaps in the backstory. He still seems to good at everything, even with the restrictions you've put in place. His motives are more fleshed out but still too powerful. Omni-tool expertise? Biotic mastery? Armor more advanced than anything we've ever seen? Killer unique powers? And he's also an information broker with a high IQ? I still think he needs to axe some things, and I think his armor needs to be nerfed. 
[list][*]Neither I nor MrD are to keen on the idea of nanotechnology armour. It seems unprecedented in the Mass Effect universe, at least on the scale required for it to resemble a black vapor when shape-shifting, and to allow regenerative capabilities. We'd feel more confident in the character if you nixed the nanite concept completely.
[*]After the explosion of his father's cargo, how did Ellis and his brother escape? You then seem to jump to his brother suddenly becoming C-sec and Ellis himself being lonely. I feel that we're missing vital elements of story here. How did his brother, somebody who was on the fast track to becoming an arms merchant, get into C-sec. I also don't think L5 implants were available to civilians, and even with them I think he would still need years of training to properly use them. MrD would know better here, but I know there is Academies and schools set up to help Biotics develop their abilities, so I don't think it's that easy to develop Subject Zero level powers. I also think your asking a lot of him in the time you've stated to become an information broker, fend of assassination attempts, develop inhuman biotic abilities, and work towards a Oxford degree in psychology. 
[*]How tough is this suit? Krogan tough?
[*]Why would he die without his suit? He didn't seem to need it before, why does he need it now?
[*]Who was the call-up addressed to originally? Is the prominent Krogan Ellis' alias, or did they intercept the message and Ellis decided to accept an invitation never meant for him? Because the final say-so of who ends up on this taskforce ultimately resides with the Spectres.
[*]So is he still xenophobic? If not, why not? Yes, Cerberus has let him down, but if he truly hated aliens so much to visit such vile destruction on them in the first place, why would the fact that Cerberus weren't quite who he thought they were change his mind on Aliens? [*]He detests tech and engineers, but relies on a technological advanced suit maintained by engineers and biotic implant? That's an interesting dichtomy. Not really a gripe on my part, just noting storytelling potential.
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I would still prefer him to be more specialized. Mr Didact suggested that perhaps he should be a former member of the Phoenix project, those were Cerberus operatives with powerful biotics. Or maybe his armor is a big hulking Terminus suit that gives him mobility with cybernetic limbs.