The only MMO I've played that does it is WoW, and it works badly there. They mess with the content tuning so it either remains trivial for max level players being scaled down with full toolkits or ends up too difficult for players who are at the intended level but only have partial toolkits. I'd not enjoy seeing it repeated here. If the content is designed around players having access to only certain abilities then it should be experienced that way when synced.

What I would like is to be able to save multiple hotbar/keybind layouts per job so when I'm syncing to lower level content I can switch to a layout for the abilities available at that level.