What I hope they do for 6e DnD

[Ignimortis]

A solution would be to actually accept that the level 11-20 are "another step", similarly to the 4e paragon and epic (but in more developed), or similarly to 3.X prestige classes (but in more systematic).
Which mean you chose an "epic class" at level 11, which actually give you either high level magic, superpowers, or maybe even stuff like "legendary king/lord".

Yeah, this. Maybe even make a class for each defined tier? So 1-5, 6-10, 11-16 (probably would be better to make it 11-15 though), and 17-20 (16-20 here). Something like Fighter into Knight or Warrior or Marksman, then those into Swordmaster or Sentinel or Sharpshooter, etc.

Come to think of it, having a base class with 20 levels is somewhat of a sacred cow for D&D. If WotC finally pull the trigger on it, it might advance the game quite a bit.