And not once has the ilvl squish occurred without some issues. Completely rebalancing not only the leveling experience, classes and world would be far more difficult. And adding another 10 levels on top of an existing frame work is trivial compared to what you are suggesting.
Now don’t get me wrong, some of what you mention I like but I honestly think Wow is getting close to being on it’s last leg and they are not going to suddenly decide to rewrite a system that has been in place for 15 years.