Disclaimer: I’m not saying this is a perfect idea, I just think there’s something to be learnt from it.
To stop having old content from being too irrelevant, what if we eliminate leveling, and only have item levels? It would avoid content from being worthless every new 10 levels and would make us need to go through all the content to progress.
For example here is how I would proportion the item levels you can acquire across all the content.
Old world dungeons/questing 1-60
Old world Raids 45-70
TBC/Wrath dungeons/questing 30-65
TBC/Wrath Raids 50-75
Cata/Mop/Wod dungeons/questing 40-75
Cata/Mop/Wod Raids 55-80
Legion/BFA/SL dungeons/questing 40-75
Legion/BFA/SL raids 60-85
DF dungeons/questing 50-80
DF raids 65-90
-item levels required for the content your doing scales in the bracket of the continents your leveling in. Ex: if your item level 35 in the Barrens the monster scales up to you and you can obtain item levels 36 item level and up.
-abilities/talents are unlocked as your item level increases.
-item level 1 to 60 is the learning phase you earn talents and abilities in this period. You stop gaining abilities and talents after.
-the item levels doesn’t have to be as small as 1-90, but it’s just the scale in which the item levels are proportioned to each other compared to all the contents. Like if Old world dungeons/questing (1-60) was 1-120 then Cata/Mop/Wod would be like 80 to 150, or in even bigger numbers proportioned that way, etc.
-Without levels making everyone more overpowered, players who have a higher item level won’t just plow through and solo old content. They would perform better but not severely overpowered.
-Also old content could be relevant to them if there was something like player housing and old content have home decorations or something like that that people can get. Or they are just there to support friends or maybe even Role playing or something like that.
-By always being relevant I don’t mean that it’s the highest content always. But that there’s always a place for the content in the progression of the player.
-I have balanced the item levels you can gain so there are less power gap between contents so people don’t over power old content and make it remain relevant when doing things like world quest or public events spread throughout the world.
-Even with a low item level dispersion, There are more epics in the raids than in questing. The item rarity is enough of an upgrade, but not too much.
-Maybe there could be a compromise and have some levels. But only for the sake unlocking of abilities and talents. There won’t be stat increase as you level. Then after level 60 it’s all item level. There’s item levels before 60, it’s there’s just also levels.
-Unrated BG/Arena brackets are 1-25, 26-50, 51-80 (with less epic loots)
Rated BG/Arena are 40-60, 61-80, 81- 90 (with all epic loots)