You can keep the cap permanent at “X”.
They introduced legendaries, Azerite etc and all they have to do is get rid of one system and make leveling attached to the next “system”. You do a zone, get to the end of questing and the main lore character for that zone powers up or unlocks one branch/tree of the next “system”.
Weapon, necklace, cape, helm, etc. Just pick a piece every expansion. I’m surprised they didn’t do something like the Lich King helm for “power” in Shadowlands.