"core pillars", says producer Garth DeAngelis, but the team recognise its importance to the community. It may happen sometime.
Mod support is something they'd "like to resolve going forward," but the team is busy with lots of plans in motion "for a while." Firaxis have just announced the Slingshot DLC adding new missions.
Designer Ananda Gupta said singleplayer missions as DLC was a "good way of offering new stuff" without disrupting the core game. Adding new tech would 'break balance'.
"If we add new weapons and new tech, then we're expanding the tech tree, and that adds research time – and that's on a fairly finely balanced pinpoint right now," explained Firaxis' Ananda Gupta. Slingshot adds three new missions available through the Council, although you'll have to start a new game to access them.
XCOM is hard on those who 'fall behind' in the tech race and so piling on more weapons and armour research would prove a problem gameplay wise, he argued. They opted, at least in the case of Slingshot, to allow players earlier access to some tech already in existence.
New content plans for XCOM is the primary focus right now for the team and so any chance of mods being supported for the PC gamer community remain dicey. Producer DeAngelis acknowledged it "wasn't one of our core pillars when we started the project," but they know it's something people do want. "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."
XCOM: Enemy Unknown supports a rather bare-bone multiplayer that could see some new content in the future also, if the community make enough noise to prove it’s popular. "We're very excited to see people having fun with multiplayer – and if that continues, we should certainly address that by providing more content," added DeAngelis.