There's already been some efforts in making one on the official RM forums. I haven't looked at the progress lately, but it still seemed like there was some ways to go.
EDIT: Looked at the two that I remembered, and they are no where near done. At best they can connect game clients together and have the players move, but that's it. They also don't update regularly nor often.
You're not going to have much luck with an MMO anytime soon in MV. No one here is going to make one either since we're either A) retired or B) work with strictly XP.