Earlier this week, id Software officially announced that Doom 4 is in the works. Aside from that, they haven't revealed anything about the game. If it's a sequal to Doom 3. What engine it will use. What platforms it will be released on, etc.
The only thing they have mentioned is that they're expanding their team and looking to hire. You can check out their official, brief announcement below, or on their main news page (at least until is scrolls away as they don't have any perma-links that I'm aware of).
"Production has begun on DOOM 4™, the next journey into the legendary DOOM universe. We are expanding our internal team and are currently hiring to work on this highly anticipated title.
"DOOM is part of the id Software DNA and demands the greatest talent and brightest minds in the industry to bring the next installment of our flagship franchise to Earth," said Todd Hollenshead, CEO, id Software. "It's critical for id Software to have the best creative minds in-house to develop games that meet the standards synonymous with our titles."
The DOOM franchise is one of the most recognizable and important in gaming history, having been named "one of the ten most influential games of the decade" by PC Gamer and "the #1 game of all time" by GameSpy. DOOM 4 will join the award-winning series which has consistently topped sales charts throughout the world.
We are looking for talented, ambitious and passionate individuals eager to join our accomplished team of developers working on the industry’s most innovative and anticipated games. For a complete listing of available positions, visit our id Careers page. Resumes can be submitted via email to firstname.lastname@example.org. All applicants must be authorized to work in the United States."