What i think would be a good idea would to have classes as an option for D&D.
A classless system can work, and it works real well for a solo game like Oblivion where you have no teammates. But the biggest thing I like about 4e's classes is the class roles (which it does so much better than any previous edition) and how it's really difficult for one character to do more than one, or maybe two, well.
When I hear someone say they want a classless system, what I hear is someone complaining that their character can't do everything by themselves. And maybe that's not the case (or at least, you don't feel as if that's the case) but that's what it always sounds like to me.
You could do a classless system that still has a strong concept of roles... but then, how is that any different, or any better, than having a strong concept of roles based on classes?