They should've never raised the level cap above 60 for expansions. Instead, for every new expansion they should've made the new content so that you could level 1-60 on the new continent (or maybe tie it into the original content where the new content was to level from 30 to 60).
This would've avoided that feeling of jumping over the small leveling hurdle (10 levels) and removed the "it's only about the end game"-mindset.
Of course they would have to look at the current 60s and what to do about them being able to start gearing for raids. Maybe they wouldve had a timed release of dungeons before opening the raids? Attunements? Maybe the wait time would make people with 60s try to level up an alt through the new content while waiting for the next instance to open up?
Also profession leveling would send players through the new content.