There was a brief discussion on Chaosforge's Facebook page about a new IP for the next roguelike. I think Kornel originally meant it as a joke, and it never really got fleshed out, but I still think it's a pretty workable concept.
Either that, or I'd choose a super-hero roguelike. Just because there's not a lot of them about. None of this progression stuff, you start powerful and end up god-like. Spam and swarm mooks at the player and have many bosses and arch villains. Sort of like a bullet-hell shoot-em-up, but in roguelike form. I didn't like the idea when I first saw it mentioned, but it's kind of grown on me. The classes and levelling system would have to be pretty flexible, and your power vs mooks would need to still make them provide a challenge, but it would probably be fun.
If anyone has ever played Sil (an Angband branch roguelike based off Tolkien's Silmarillion), then combat could be similar to that. One on one, you're tough. Get swarmed or mobbed an you're screwed. Positioning and tactics could be key, even with your super-powered status. Resources based off class, perhaps ripping some of Diablo 3's concepts for different classes. Just done properly and more interestingly.
Wouldn't make a bad game I think.