Someone at Bleeding Cool had an interesting theory. J. August Richards could be playing Michael Collins (aka Deathlok). It's clear in the trailer that the tv character has some kind of cybernetic implant in his arm (possibly alien tech that could be spreading over his body with time?); and the Collins Deathlok from the comics had assistance from SHIELD in improving his condition.
All just theory, though. It would take a different interpretation of Deathlok to make it work, but there's a great deal of dramatic potential (especially if the character dies but the tech brings his body back akin to the corpse like Deathlok). Can Michael find his humanity again after that? Lots of dramatic potential; and the kind of surprising heartfelt twist I would expect from Whedon.