Not sure if there's a game that does this already but if I ever made an MMO, I'd try a business model of open source server and client and compete on paid hosting. Minecraft sort of has that going with realms but closed source and centralized accounts. Both of those have been circumvented with the Java code but the C++ based version is the future and the Java code with eventual get feature freeze.

Edit: Now that I think about it, this is pretty much the same as the current business model for many development platforms, open source tools and cross platform support, compete on hosting.