What is Epic Games' next PC exclusive?

At PAX East last weekend, Epic Games president Mike Capps revealed that the developer "might be working on a PC-only title." Cliff Bleszinski was less ambiguous, responding: "Let me say that again: we are working on a PC game."
So what is it?

So what is it? Some rumors pointed to Fortnite, which was announced during Spike's Video Game Awards late last year. We know little about Fortnite, except that it's a Minecraft-inspired monster defense game with a nifty trailer. On his LinkedIn profile, Epic Games producer Chris Mielke stuck a "(PC)" onto his mention of the project, but that distinction has been removed, and Capps told Joystiqthat the PC exclusive is unannounced.

The most obvious possibility is Unreal Tournament 4. We heard before the Game Developer's Conference last month that Epic would be showing off Unreal Engine 4, and history suggests that a new engine means a new Unreal game. Given the impressive results Epic is still getting out of Unreal Engine 3, however, the release of UE4 could be far off. Perhaps the "Samaritan" tech demo from last years' GDC will become a real game first?

Or maybe it's Jazz Jackrabbit 3. What do you want to see from an Epic-developed PC exclusive?