If you are the DM mix things up abit. Tell everyone that nobody can play a PHB class...
I haven't DM'ed in almost 2 years, largely due to a combination of FRPG adventure-design burnout/writer's block coupled with a group that only wants to play D20- and D&D in particular. (As I've mentioned in other threads, few of them are even interested in anything beyond the Core + Completes, several dislike even the notion of Psionics, and most are completely unwilling to try 3rd party products.)
I have lots of ideas for other RPGs- I have 3 fleshed out campaigns just sitting around, designed for Modern Fantasy and Superheroes/Sci-Fi, but I have no takers.
However, for the past 4+ months, I've been designing a new FRPG campaign- something that I think is pretty special. While it won't really affect the guy in the "All Rangers, All the time" rut, the guy who only plays wizards may find himself re-evaluating his default choice, even though I'm not eliminating any of the PHB classes.
Of course, there's no guarantee that anyone will want to play
it either.