Hmm. Wild speculation time.
What if it is, canonically, an alternate time line? They made a point that the volunteer survives the Temple Ship. What if the Volunteer ends up showing up sometime during XCOM-2 to help out this universe where the aliens won? Maybe kickstart X-Com's psionic potential up a notch?
That...could be really cool, if done right.
That... would actually be hella neat.
I wonder, since it was user-selected, how they'd make a specific volunteer canon, if it'd just be an all-obscuring armor or the like, or if it'd just be something generated.
...
I wonder if that has to do with the introduction of guaranteed canon psychics from Progeny, Annette and the Furies, but especially the former. Otherwise, there's always save-game imports, but...
Class speculation: Assault, Heavy, Support, Sniper, Ranger. Drone might be tied to a human controller on the battlefield, given that it appears on the (human) class group shot, or a SHIV-type combatant like I originally speculated.
Finally, I actually assumed that those were well-defined pecs or armor. Terrestrial snake bodies aren't exactly designed for upper limbs, after all, and it appears to be largely snakelike except for those arms. It could have been added on after.
((So many replies in the warning notification...also, edited some clarification into the above.))