Would this be something people would welcome? The idea being that once you get to max level, you can continue to gain xp and lvls but rather than this applying to that character, it creates a reservoir of levels that you can grant to alts. Rather than having to say take time away from raiding or whatever else you're doing for 95% of an expansion's life-cycle you can do that, and also create a new alt. Players being inexperienced at playing certain classes could well be a problem, but the system could be restricted so you can only grant levels to a class providing you have another character of that class, at that level.
Not really sure if I'd be up for this myself but it's a thought I just had.