While he's not saying that that's what they're doing, Mark Jacobs stopped by the Warhammer Online forums to say that they're not adverse to shelving a few classes before release if they don't pan out.
In terms of the number of classes, marketing, release, etc. It's still pretty simple, we'll release it when it's ready but keep in mind that beta is for chucking what doesn't work in order to replace it with stuff that does work. So, if a class doesn't work out the way we hoped it would, we *might* keep it out on release if we can't come up with a good way to fix it. It would make no sense to either release the game with a broken/bad class or to hold up the game's release if we are not sure even how to fix a bad/broken class. One of the lessons from DAoC's development/evolution was that less is indeed sometimes more. Again, please don't read anything into this post other than the usual "this sort of stuff is what beta is for" disclaimer. Besides, with the new systems we have been putting in, players will have even more options to customize their class than before so I don't think players having a dearth of class/options is something you have to worry about.