They're already busily working away on the next TES, and the next Doom was already in production as well afaik. It'll either be the engine for the next TES or, more likely, their own engine (
id Tech 4). ID didn't loose all their independance, they just gained the ability to do without publishers like Activision. Really, this is a win-win, that's why it's such great news.
I hold some (possibly idle) hopes of Beth cobbling together/acquiring a new engine to make proper use of multi-threading, the old TES engine really was at it's end IMHO;
Gamebryo engine has been around since 2004. Brink is being worked on as well, and even though Fallout 3 proved Gamebryo could pull of a FPS style game, I think (or is it hope?) Brink will be using something different.
*maybe
Emergent Game Technologies put together the successor to Gamebryo already... anyway, next Doom will be running on id's own engine.
