Hey guys, an idea popped up in my mind and I would like to share it here.
A way to fix the leveling experience without revamping the existing areas can be if Blizzard introduces a new spell called “Training chamber”. This spell should come at level 10 and will open a new dimension where the player can go through a series of trials and with each of them gain levels.
They can enter and exit at any time, but only when a specialization is selected at level 10.
The trials should be training that teaches you how to use the selected specialization.
For DPS trial examples can be:
- Kill a group of mobs without dying
- Kill an elite mob and use the defensive skill at some skill
- Kill a raid boss and don’t stay on the fire
- Use interrupt/stun at the healers
For healers, examples can be:
- Heal single target
- Heal a party
- Heal a raid group
- Heal and interrupt/stun
and so on. In general preparing you for what is waiting for you when you finish the trials.
The trials end when you hit a level enough for the latest expansion and this should be done in 4-8 hours. It can sound short time, but nobody like to dungeon queue the same dungeons again and again, and everyone wants to go to the end content these days.
The player can enter to practice each specialization separately even after completing it.
When a player switches from a DPS to a healing spec for example, usually gets overwhelmed in the first few hours about how the new spells are working and so on. The “Training chamber” can be used in this situation as well.
If you like the idea or have ideas on how to make it even better share them here. Maybe one day we can see the “Training chamber” to become a reality 
say, have a popup quest that clearly states this is meant to teach them.