I'm kind of hoping for a completely new arc starting in 7.0, with an alternate intro for maybe 1-20 and a level-scaled MSQ thereafter with no requirement that every player go through ARR to Endwalker to reach 7.0's endgame (though it'd be useful for alt-leveling, etc.). Player levels would probably be squished down to 50 and then some build choice involved over the level cap extensions thereafter, as opposed to the classically bloated 2 actives and 3 passives (or what will later be sensibly reduced to passives, as per BotD or Enochian), as we increase from there in increments of 5 or 10, depending on the number of expansions to go before XIV's grave.
* Ideally, I'd like that build choice to flesh out the "all jobs on one character" concept a bit further or maybe even give further purpose for revisiting past content (as a form of horizontal progression).
