With no true setting support to keep fans of previous settings or to inspire people new to the game, it may cripple the long-term viability of the line. The 3 and done model for settings will, IMO, prove to be incredibly short-sighted.
Having said that, again IMO, any prospective 5e isn't likely going to be done by WotC. I truly don't see them doing it unless the 4e line collapses utterly and they reverse design direction on a great many things. But if that happened, I would expect Hasbro to simply shut down the RPG division and hold onto the IP.