I can sort of understand the desire to play as one of the other race's.
However The whole aspect of this game has sort of been how humanity is the paste that glues the messed up galaxy back together, so I don't see any good way to branch out, and make the commander be another race.
I am not saying it could not happen, it would just not fit the trend of the game's as they have been portrayed up to now. ( I don't think ).
With that said, I think there might be some [ providing you can get past the fact that two races born, and evolved in two totally different environments could breed ] room for a hybrid that would be easy with the Asari, but of course that would actually be Asari, genetically they would have no Human in them [ if I understood the fictional process right ]. But say a half-bred Human Krogan, or Turian, or Drell, or Batarian, Elcor, Prothean, Hanar, Vorcha I guess you might be able to write something like that in. But it just does not seem the right course for the game to me [ But that's just my Opinion,( don't go spreading it around ) perhaps you should talk to a people person ]