I don't think I've seen this discussion hashed out since the leveling revamp was announced, and that surprises me.
So... I don't know where I got the impression, but it's in my head from somewhere that Ion Hazzikostas was put where he is partially to future proof WoW for the perpetuity that, really, they never expected for this game, once and for all. Whether that's his doing or not is debatable, but it's absolutely a thing that's happening.
As much as he claims not to want things to get too formulaic, you can see these efforts here and there: Flight/Pathfinder is an expected formula now, the patch cycle is relatively standardized with some wiggle room, legacy loot is a hard coded and necessary promise for those playing the transmog long game, and our expectations between main patches and "point five" patches have formed a straight line that has us anticipating timewalking right on time each expansion.
So let's look at the leveling overhaul in this vein.
You have your starting area bracket, your "legacy content" bracket, your "immediately prior expansion" designation for a smooth transition for new players being told a flowing story, and then your 10 levels for the current expansion. Pathfinder becomes something you do at the X.2 mark if you wanna fly in current content while it's current, and that achievement becomes of lesser import by the time that content goes legacy if not in the immediately following expansion. That's all very neat, tidy and as soon as we live through it once, going from 60 to 50 to climb it again, it's precedent.
...And it potentially happens again, every two years, as everything slots into its new place on the climb from 1-60. On schedule. Forever. Or as long as the game keeps going anyway.
It's so elegant it seems a sure bet at this point. How the hell does a "level 60-70" 10.0 even fit into this? It doesn't. We'll be 50 again for 10.0, Shadowlands will be the non-optional 10-50 game for new people, and BFA goes fully into the legacy pool of leveling options for veterans.
That's gotta be how this is going, right?
Right?
To be clear, I'm not complaining, but I haven't seen this accepted communally, this... nigh inevitability I'm seeing unfolding here.