I would love to play in a game like this. I am not sure how I would react as a DM. I would have to dial the way I normally think about DMing back and hand more creative control over to the players. I feel like this could get very silly if people were in the wrong mindset for even one session...
I will play Numenera as soon as I get my hands on it. We will probably keep playing Pathfinder for the time being, too. I would be interested in 13th Age, as well, if I had the time.
We play in one Pathfinder game, and I run a solo D6 game. We're about to start another Pathfinder game to teach some coworkers the rules. Other than that, we do board games with different groups of people on weekends. I would love to have more organized games, though.