I'm kind of committed, but I'm still not sure exactly what I want to do. I'll figure it out, likely at the last minute, but right now, not sure.
I'll probably use 4e D&D. I'm not completely, absolutely positive about that -- it's not like 4e isn't going to get plenty of support besides me -- but it would be the most efficient use of my mental energy. I'm running a 4e game, and I'm sort of obsessed with it, and there are a lot of things in it I want to play with.
Actual subject matter is a lot more nebulous. I might do something like Asteroid 1618, or an encounter-filled hex map. Interesting places to explore, rather than a sequence of events, and trust the DM and the players to make some fun of their own. It'd be a lot easier than trying to plan out any kind of plot, without players to provide all that agency stuff for me.
I've changed my mind about topics a lot already, though, so I don't know how long this will hold. I might just end up doing Fall Off the Shadowkeep, or some kind of fantasy survival horror scenario.