WoW has historically been about spending your time in the latest expac and only going back to farm things. But is it time to revitalize the older zones by introducing worldwide-level scaling?
If quests/NPC’s/loot etc. all scaled to you no matter where you went, it would mean that ultimately gearing would be redefined. The devs instead of making new gear which becomes obsolete next expac, could invest their time into making more permanent gear which can be upgraded every expansion.
This is just an example but maybe something like, 1 “legendary” gear set per class thematically designed for that class. This gear could be upgraded with the latest runes/enchanments etc. that an expansion provides but these drops would only happen at the latest content in the hardest content (raiding/mythic/arenas).
Every expansion would bring new thematic forging to this base legendary gear set that can alter how the armor looks but from a power perspective, the latest expac just modifies the power capabilities of the armor to create a synergy with your class (maybe even bringing more utility with it).
Meanwhile, players who do NOT want to participate in “end-game” content as we know it today, would still be free to roam around the open world now scaled, and all other gear items, assuming player is max level, would just scale to the next ilvl below this legendary base set, but never above it.
This would allow casual players to participate in things like heroics, maybe non-legendary arenas, and still “play the game” while not having to invest themselves into end-game content to keep chasing the power.
Hardcore gamers get their permanent gear system that keeps building on itself both vertically and horizontally, and casual players have the entire world at their fingertips now scaled to them and everything becomes relevant again.
This means professions/crafting would make a huge return as well. For players who like to run old dungeons/raids for mogs/pets/mounts, the devs could have a “legacy” version of these instances that keeps the original scaling as it exists today. Only less broken (looking at you legion).
Lastly, a permanent system for casual players to compliment the permanent gearing system for HC players would be player housing.