I think it's a great idea (well, see my above comment :)! Keep the scope small - this doesn't need an MMO to be successful, make it single player. Start with text and find an artist along the way.

On my walk home between posting my initial comment above and this one, I started thinking about how to make it happen as a side project and the conclusion I came to was writing the entire script/story out first as that would be the hardest part.