I think the logic on this is backwards. The time-limited rewards that should be protected are the ones that required some degree of group effort to earn together (Mythic raiding, m+ dungeons, Arenas and BGs PvP, etc).
On the other hand, it’s exactly stuff like solo challenge rewards that would make much more sense to allow a new generation of players to try and earn - at the very least some kind of re-color. And let’s be honest now, Mage Tower was never that difficult, certainly no where close to the difficulty of Mythic raiding achievements.