Probably the biggest bombshell to drop today at Blizzcon regarding WoW's upcoming expansion is the fact that the level-up zones and dungeons will scale to our level.
Using some of the technology designed for Proving Grounds and Timewalker Dungeons, you'll be able to go into any of the four leveling zones: Highmountain, Stormheim, Val'sharah, and Azsuna, and play through them in whatever order you want. Enemies will scale to you, rather than having you scale to them, and your quest rewards (and presumably item drops) will scale with your level.
Each of these zones will have non-scaling max-level creatures as well, so you'll have to come back at 110 to fight them.
This could mean the end of bottlenecks at expansion launch (though it will still all presumably be on the same world server.) Also, somehow, you'll be able to group up with a friend who's five levels lower than you are and be able to do the same quests. I have no idea how that's going to work - like if you see a different health bar than your buddy - but this could be fantastic - effectively using the Elder Scrolls' leveling world to let you do things that interest you.
If this system winds up working out well, you could even imagine doing this with the older zones. Imagine, rather than going to Outland at 58, you might go do the other old world continent. Hell, this might make out-leveling zones a thing of the past!
But let me not get ahead of myself.
Suramar will be a level 110 only zone, and there's another zone that, Tanaan-Jungle-like, will be on the maps but not available until a later patch.
This also means that all zones will be max-level zones once we hit 110. Daily quests are going to work a bit more like they do in Hearthstone and Heroes of the Storm, meaning that we'll be able to bank up objectives if we can't log in for a couple days.
It really looks like we're going to see a lot more scaling content (including Challenge Mode dungeons, which are set to be a true alternative to raiding) that should provide people with a lot more to do.
I really hope it all works out well.
EDIT: Another rather obvious now that I think about it implication of this? Once you've hit 110, everything in the Broken Isles will be of an appropriate level, and so the outdoor content of the expansion will be able to remain relevant, at least until we're all super-geared. This will make getting your exploration achievement a little more difficult, sure, but in return you get a vast continent of potential daily quests and such to play around in.
I think that this system could really make the game play more like a thriving, existing world rather than the set of locations that are only relevant for particular stories that we've gotten in the more linear, Cataclysm-onward era.