I'd actually like the ability to test our other classes as well. Of course, only in a training area with a dummy or three designed purely for testing not dropping you into the live game. Sure it would remove the natural learning process but the OP is right in saying that you just don't know how a class feels to play at higher levels until you've actually done it. And if it was purely a test situation I don't see the lack of experience being a real issue. It would just be a controlled solo environment and once you selected the class you'd have to start at level 1 just like everyone else.
