Well, here's the thing. To my knowledge there have been two completed RPGs (that I'm aware about). It's sort of silly to make a sub section that isn't going to be used very often. You've sort of already laid out your answer. RPGs do take much more work to complete and there's a lot of factors going into that, the most obvious being that it's a group activity which means that when one person leaves it could have a potentially crippling affect on the RPG itself. It's a lot more practical and used for fanfics because they get completed a lot more. Also this idea has probably been suggested enough times and the answer has always been no.