Just some tips for you from a guy who failed badly at making an XCOM RP. Try to keep it simple and economical, otherwise it would be too much to handle and the moment something in real life comes waltzing in, it'd fall apart. With XCOM, it seems tempting to make the RP as epic as possible because, you know, it's XCOM, so I guess while this tip applies to alot of RPs, it's gonna apply especially to XCOM.

On a more positive note, when I presented my own set of ideas (somewhat similar to yours), people do love the idea of a contemporary XCOM, and one that goes through the origins of the organisation. They seem to like the idea of starting out as an organisation that barely is, assaulted from all directions by problems with funding, getting enough (competent) manpower, or even trying to function from day to day. In my XCOM RP, politics is a real problem, the ruined world economy with the US becoming third world and China becoming really rich is a real problem, and the UN viewing XCOM as a very minor branch of itself is also crippling.

Also, alot of mystery, alien-ness and deadliness to the aliens seems to be well-liked too, rather than having aliens that could be dispatched by primitives who are outnumbered two to one. I'm talking about turning the tables, and instead having aliens that could win even when heavily outnumbered.