Raids inbetween leveling phases
I'd really like to see a raid somewhere around level 35–45 in Classic+.
I think that level range would be perfect for it. The early leveling experience in Classic is paced pretty well, but somewhere around 35–45 it starts to drag and there's usually a lot more grinding involved. A new raid alone could make that part of the game much more interesting.
But more importantly, I'd like Classic+ to make the whole leveling journey feel more like an actual adventure and less like something you just have to get through to reach 60.
Right now there's often no real reason to chase a great item while leveling. Why spend an hour finding a group, another 1–2 hours running a dungeon and maybe not even get the drop, when you know there's a guaranteed quest reward five levels later that's better anyway?
I'd like Classic+ to give us more reasons to actually care about our characters while leveling.
A level 40 raid could be one of those reasons. And I'd want it to be genuinely difficult at the intended level. Something where you actually want good gear, enchants, consumables and have to know your class. Give people a reason to optimize their character at level 40 instead of only thinking about getting to 60 as quickly as possible.
The rewards could also tie into the later game. Maybe there's an exceptionally strong weapon, a class quest, a token you can use at 60, or even an item that's still good pre-BiS once you reach max level.
Basically, I'd like the transition into endgame to be more gradual. Level 60 shouldn't be this hard cut where almost everything you did and collected before suddenly becomes irrelevant. Some of the things you accomplish while leveling should already be part of building your eventual level 60 character.
Most importantly though: it should be optional.
I don't want every alt to be forced through a level 40 raid because you need some mandatory item or token to raid at 60. You should always be able to skip it and continue leveling normally.
It should simply be another difficult and rewarding adventure for people who want to do it — and another reason not to treat 1–59 as something you just rush through.