In my personal preference, I think quests and open world engagement during the leveling process is important, it should be fun to log in at all times and feel like I’m doing my very important job curating Azeroth.
My take is through the lens of trainers, I think more class trainer quests- perhaps at levels where major zones open up could serve as a great transition to a new zone, maybe with a new item attached to the quest
For example: (These are random numbers) let’s flare is learnable at 44---- get quest to use flare somewhere in Tanaris, this also pathways the character into a new zone which is good for new players— come back quest reward is item and/or learn flare for free which could help ecologically since there won’t be any gold bots or sellers and those little bits of gold add up!
The thing I remember most about classic is really the little things that were cool and made a lot of RP sense rather than huge designs, new raids and dungeons are cool, but please forget not the little nuggets within that make the experience from 1-60 super engaging to the brain
please more ideas in the chat!