You uh... you missed the point there, Sparky. They *wouldn't* be developing 4 systems. They would be inventing 0 (zero) systems. They would, instead, be producing content that worked across all the previous already existing systems.
TSR failed because they produced crappy setting after crappy setting (Red Steel, anyone? "I must have the Cinnabril now! *pew!pew!* ... awful. >.<) not because they tried to do what I am proposing - they never did that.