The next project was to be Doom for the SNES, but in making Wolfenstein for Nintendo, all that changed. Wolfenstein for the SNES was technically very easy, it was Nintendo that made it hard. Nintendo had Id remove the Nazi imagery and change the German Shepherds into giant rats, which wasn't a problem. Over the next couple of months, Nintendo picked over little details and frustrated the Id team to the point that it dropped all future SNES development.
The console system that Id is now looking at is the Atari Jaguar. The Id designers were very excited about it initially and were going to develop for it after they completed the SNES version of Doom. Id is betting that Atari will ship over 500,000 Jaguar consoles. After their experience with Nintendo, the Id designers decided to primarily work for the Atari Jaguar.
After that, it's off to work on the next showcase game. The subject matter hasn't been determined yet, but the technology has. The next game engine will have true three-dimensional perspective, where detailed objects can be viewed from any distance or angle. If the Id team can keep its high standards of performance and playablity, maybe it will feel compelled to take it easy for a while, but don't bet on it.