I think that might be the best thing to do at this point. Here is the manner I wouldn't mind seeing it done:
Level 1-60 as it is now.
Outland-Northrend becomes paragon level 1. Maybe squish the xp needed to get there down to like a million or something like that for each paragon level.
Cata-Pandaria becomes paragon level 2.
WoD-Legion becomes paragon level 3.
BfA would become paragon level 4 or gets added into P3 content.
All creatures in the world are scaled down to lvl 60 in all of those zones.
The next expansion we level up to 65. No more 'omg 130 levels' for people who are just trying out wow for the first time. Less time leveling for everyone else. Profit?