There were some interesting comments on the May 14 Dev chat appeared recently. One of the comments that caught my eye was a question regarding keeping lower level content relevant, particularly Veeshan's Peak (so Mythicals retain some relevance.) A dev responded that they were indeed looking into ways to keep lower level content relevant. Unfortunately, they provided no further details...
I don't know what they have in mind, but one idea that I would like to see would be for zones to automatically mentor people who exceed the intended level range of the zone or raid by several levels. It might be acceptable to allow people to "outlevel" a zone by a few levels, to maintain a sense of progression, but to completely gray out and trivialize zones robs the game in the long run. No one ever wants to go to these old zones because there is absolutely nothing to be gained. Keeping the older zones at least somewhat challenging prevents many quests (where you simply travel to certain parts of the zone) from becoming completely trivialized, and therefore less fun.
I'd also want to see level scaling zones automatically mentor a player down if they exceed the level that the zone was set to. For example, if I mentor down to a level 50 and zone into Scion of Ice, the zone sets itself to level 50. If I then unmentor, I should be forced to remain at level 50 (even though I'm no longer mentoring anyone.)
These days, mentoring seems to be used most often to exploit game mechanics by trivializing zones. It was intended as a way to help veteran players join forces with newer ones, and to work around one of the principal disadvantages of a leveling system: leveling creates barriers that prevent people from playing together.
To help encourage high level players to join forces with low level players for mutual gain instead of exploiting the game mechanics, I would also want to see them increase the amount of XP you get while mentoring, almost to the extent that one could level from 81 to the next level cap on OLDER content if one wanted to (obviously the newer quest lines in the newer zones would be better since you'd gain better gear and so on that way, but the point is it gives people a choice and makes mentoring a mutually beneficial relationship, especially if the higher level player isn't earning AA from it [because they aren't at the level cap, for instance.])
This would make it more attractive to play with lower level players for both AA and leveling up (when they increase the level cap), without completely trivializing the lower level content (obviously the mentoring scales imperfectly, but to some extent that's fine.) And it would help keep much of the older content in the game relevant.