Alternative: Keep Limited Jobs, but make it so that they're not 20 levels behind. Lagging behind one expac would be enough to keep the previous content decently relevant.

Also, give Limited Jobs more things to do. Being gated out of things like MSQ and Squadron is silly. And if you're worried about BLU cheesing Deep Dungeon, then make it so that Deep Dungeon records don't count for BLU since it's easy mode. I don't mind not being able to use Duty Finder so long as I have access to reasonable amounts of content, not just old dungeons I've gotten bored of or Trials/Raids I need to wait for seven other people to join my PF for.