I don't have a lot of mental energy to devote to RPGs right now, so I'm presenting this as a bare-bones idea. If anyone wants to take it and flesh it out, modify it, or fold, spindle, and mutilate it into something else, feel absolutely free to do so.
It's often said that high-level D&D is about domain-level play rather than dungeon crawling and fighting ever-bigger and badder monsters. High-level play is also plagued by breakdowns in game mechanics as hit points, attack rolls, saving throws, thief skills, etc. continue to grow with each level.
Well, how about all those things max out, or at least slow down drastically, around name level? Characters don't get too much better at bashing monsters after name level. Instead, each class starts building abilities and skills appropriate to domain-level play.
Fighters get bonuses and special maneuvers for leading armies in mass combat.
Magic-users and clerics learn magic rituals that affect entire domains and may last weeks or months, but consume large amounts of resources and take days to cast, instead of just getting bigger and flashier guns to fire off in a combat round or an exploration turn. That would require writing up a new list of high-level spells. Maybe all spells of level 7 and up are of this type.
Thieves could become skilled in political subterfuge, intelligence gathering, maintaining a stable of alternate identities, etc.
I don't have any specific game mechanics yet, but it seems like this might be a good way to keep high-level play interesting and keep level advancement relevant without breaking the power curve too badly.