Eventually 5e sales will flag and they'll think it's time. If there are other much loved innovations in gaming at the time 6e will be more different if not it will be a slight evolution. Most likely though, having been burned on making radical changes for 4e, whatever new edition will probably have some pretty incremental changes.
But as I write this Amazon's #17 bestseller is the Eberron book. The PHB is #143 and often cracks the top hundred. If you don't want change the solution is to keep buying stuff and keep getting new people to try the hobby. As long as the PHB is a perennial Amazon bestseller and supplements aren't flopping they probably won't change it.
As for whether I want a 5.5e or a 6e, I'm satisfied enough with so much of it that I think I'm happier with the devil I know then risking whatever crapshoot may come next, barring the unlikely scenario the WotC decides that I personally should design a new edition.