In a recent talk with Joystiq
about the upcoming XCOM DLC Firaxis are still being annoyingly tight-lipped and non committal on modding support for XCOM.
As for the future of XCOM, Firaxis is open to the possibilities. Regarding the potential for mods and user-created content, DeAngelis notes that "it wasn't one of our core pillars when we started the project," but the team understands how important it is to the community. "It's something that we'd like to resolve going forward, but we still have quite a few things on our plate that have been planned for a while."
If you're cynical, like me, that reads as "we'll maybe talk about mods after we've milked the DLC for all their worth". Not that you can hold it against Firaxis. After all, they're a business. But for people who care more about mods than they do about lacklustre DLC it's a blow.
In other modding news, modders have been making inroads in to modding the UPK files
for XCOM. While there's little progress on being able to repack the UPK files themselves, advanced modders have been able to mod the UPK files and get them to load in their games. Unfortunately the process is relatively complex and there's no easy way to distribute these mods to the masses. Yet. Work is underway to change that, however, and with Firaxis being less than helpful on the modding front for XCOM thus far this is going to be our best bet at modding the game at least for the foreseeable future. Stay tuned.