The question that you have to ask yourself is, "what is the blockchain bringing to the game design?"

That answer needs to be something broader and more useful than "it's where the posting community is," because there are a lot better places for carrying on structured communication like a play by post role-playing game than Steemit. There are places with specific support for mechanics, there are places with their own mechanical resolution systems which work just fine for the most part, there are options.

If your answer is "because all the participants can get paid a little bit from all of the other participants and their up votes, assuming that they create good content for the game" – I would respect that. That's perfectly reasonable. But beyond that, I'm not sure that there are a lot of meaningful mechanics that the steem blockchain actually supports.

Give that some thought. Let those ideas percolate.