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I've done some testing, if anything I levelled faster. There's a much more natural curve now, you just plod on through the quests. you never have to run across 1/2 a zone to get to the next one because it's not worth doing the quests anymore, you can just do everything and follow the intended questing path, which is insanely efficient. at the absolute max you are running for 1 minute to the next hub, instead of 15+ in most cases.
The fastest way to level 1-60 right now is to quest and do specific dungeons (only once for the quests). Each time you come out of a dungeon you are pretty much guaranteed a zone swap, you are chasing zones while queued because you outlevel zones before even reaching them this way sometimes. With the changes? You'd be able to queue up for dungeons while questing westfall. Come out after doing DM and RFC at easily level 17/18+, and still do wesfall instead of having to run to redridge. in the time it would take you to run to redridge, you'd be able to run BFD and hand in the first bunch of quests from westfall, that would put you around 20, and wait... Your still in wesfall. you finish westfall, go straight to duskwood probably around level 25 now, skipping redridge completely, and avoiding that 20 minute run. you've generated XP in the 20 minutes you saved, avoided a long and boring run. Finish off duskwood and do the other available dungeons, the scarlet monastery ones. Bam, your level 30+
after duskwood, because the questing path brings you close to redridge, you can go there, even though its a 15-20 zone, because scaling! This is where I stopped, because I was convinced without a shadow of a doubt that this was infinitely faster.
I got from 1-26 faster as a human on the PTR than I can on live, and it's all because of the scaling and the reduced running times. I've yet to test the difference with heirlooms / the chauffeur. I suspect it would actually make the difference slightly bigger tbh, after discovering the massive difference not running to redridge from wesfall makes. Heirlooms will likely make you leave RFC / DM at 20+ as it does on live. I intend to test this, but I think it may be possible to continue straight onto burning steppes after redridge on the route I did. Searing gorge afterwards.
A thing I keep seeing people miss aswell, although XP requirements are going up, XP gained is going up, possibly more. Imagine you are in westfall, which is a 10-15 zone. At level 10, the quests give you 100% XP, but at 11, they give you 95% (Comparatively - XP requirement goes up, reward stays the same) with the scaling, every quest you ever do is 100% XP, it's as if you are the minimum level for the zone, even if you are 30 levels beyond that. If you have 3 quests to turn in, and the first levels you up, the tooltip on the other 2 bumps up the XP reward, to the point where it fills almost the exact same % of a level.
Needs confirmation but Elwynn -> Westfall -> Duskwood -> Redridge -> Burning Steppes -> Searing gorge. With each dungeon done once available - may be possible. That would line you up to continue straight onto Outland / Northrend, and take maybe 4 hours? 5? With the scaling Dragonblight is just going to be an XP orgy, Sholazar too. both zones are extremely good for XP, which is why you only do 1/4 of them before leaving on live. You can do both to 100% which would easily be 10 or more levels. I'm happy to assume 60-80 would be faster due to those 2 zones alone. Then the glorious Jade forest time, the difference is, now you can fly there at 80. and the XP would potentially be even better than it is on live, because the "always 100% XP" thing I mentioned. You'd possibly get more than the standard of live, which is 85-90 (the entire MoP levelling from the first zone). it's safe to assume you can get 80-85 as a minimum. I'd bet you can hit 86 or 87 though. You can now go and do any pandaria or Cata zone until 90, at which you can go to Draenor. Assuming the good old Gorgrond XP orgy is still a thing, your gonna be level 100 30 minutes after you land in your garrison at level 90. From here, it's the same as it is today in the Broken Isles.
I don't know how long 1-110 is going to take, as I've not done it, but I'm gonna guesstimate it to be considerably less than it is now.
The beauty of this is, that although I found levelling itself to be faster, combat time is maybe, 3 or 4 times longer. You can do a full rotation at level 20, which is really nice, since you one hit everything upto level 100 with heirlooms normally.
This has my seal of approval, and I'm looking forward to the allied race's. Levelling is so nice now, I'm almost disappointed they start at 20 instead of 1.