While on the subject of wishes and fishes, I wish they would do a couple of things to Azeroth going forward. First would be update a lot of the assests in the 1-60 zones. Drag the game kicking and screaming out of Vanilla. Fix Stormwind and Silvermoon. Let the Gnomes re-take Gnomeregan already. Integrate the Draenei and Blood Elf starting zones properly into the world. Second, if it turns out to be a good thing, would be to add the level scaling that's in Legion to Azeroth's 1-60 zones. Let people quest where ever they want rather than going through the same paths through the same zones over and over. Third would be to add public events that are thematically tied into the questing of the zone and unlock after you complete the questing and exploration achievements for that zone.
If the level scaling is there, you could be dropped down to the max level of that zone, sort of like Time Walking events, or Legion scaling could be applied so the challenge is appropriate to all players. These public events could provide valour points or some other currency that is a viable reward for players of all levels but maybe only used once you're max level for gear. Or it could be another avenue for leveling players to earn heirlooms,
For example, Bilgewater Bay is supposed to be the Goblin capitol that replaces Kezan, right now it's home to like 4 or 5 quests in the mid-point of questing through Azshara and that's it. You clear those quests and never go back. What if once you clear the Azshara questing and exploration achievements you unlock the public events, like defending Bilgewater from a Naga invasion. Or needing to defend the border from a Night Elf invasion. Each area could have two or three public events loosely based on the over-arching stories of each area. Contested zones public events could be world pvp, although I have no idea of how they would handle that.
I know that Blizzard's approach has been to speed people up through leveling fast and faster with heirlooms and level boosts. But with the 90/100 level boosts, there's a reward for getting your toon to 60 first. Public events would be another way to make the earlier questing zones viable to high level players and maybe feel like more of a living world for everyone. I know there's profession mat farming, archaeology and pets but none of those are group activities. They could tie valor points, some titles and achievements to it, maybe even a mount to completing public events. And they don't need to add it to ALL of the game, just Azeroth.
Sorry, I'm rambling.
There's no way they'll put significant effort again into the old world. They seem to already regret the resources that went into the remake for Cata as it is, and they've barely bothered to touch the old BC quests at all. Maybe you'd see some sort of universal scaling system put into place, but the idea of going back to old zones and being overpowered is such a long standing part of WoW that I don't know that they'd ever think that was worth the trouble. And it would have to be something they could just blanket add with minimal additional zone tweaking needed.