Sounds interesting. I'm into collaborative fiction and this sounds a bit like that. The world building part reminded me of a game I played called Microscope where you play out scenarios to answer questions about the history of world you are building. The scenarios are a lot like role playing but in every scenario you play a different character. I enjoyed playing it and would be glad to try it again but like Spark, probably not for everyone.

This is like RPG meets collaborative fiction with a dash of improv, yes. Not for everybody but definitely for me. :)