Game could benefit a lot of going back and standardizing the markers for ARR and early HW to teach them properly to people. There's some really wonky stuff like WoD markers, Sohm Al markers etc. that are different and at worst the opposite of what they are later. Having to second guess stuff because the game didn't properly teach them early on can be frustrating to newer players and even older ones that revisit the content.

Having the Hall of Novice updated or having secondary one later for common mechanics would be beneficial.

And as others have also pointed out, tightening the difficulty close to what past content was on release would be nice as people don't really get the same feel for it with all the skipping and ignoring mechanics.

Base level of difficulty for normal content doesn't really need that much change as long as the past content gets the respect it deserves, additional midcore and maybe even some hardcore content would be nice as long as it doesn't cut out too much from other stuff.