Since the start of Autumn, there have been plenty of rumors regarding the roadmap of Valve. The company keeps silent on the upcoming projects, even on the existing ones there is hardly any information.
The claims that Source 2 engine is nearly done seem to be kind of too early. On the other hand, multiple sources reported in October that Valve plans to release an FPS game, with the lore of Dota in mind. Seems like this project has been in works even before the release of Dragon's Blood anime.
Now, one of the trusted insiders, Gabe Follower, has hinted that Valve's Neon Prime is not what it sounds like. By his logic, Valve don't have enough work force to do multiple projects at a time, so the so-called "FPS game" might be the part of the multiverse.