Or they could just finally revamp rewards instead of just relying on roulettes and Moogle Troves. No reason to do old level cap content since you get no exp and you can get loot by unsyncing it, trials basically give nothing, non-CT AR take 2 times longer while giving same rewards (if you don't want specific glam). Even though Swallow's Compass is one of the best dungeon in game, you see it once a year in roulette since it's at old level cap, not in free trial and optional.

Current implementation of Moogle Trove is pretty bad anyways, since you can just use blue mage and be 10 times more effective, which won't help DF. There is also this kind of "battlepass" you speak of in form of Khloe's book, but once again, you can just do 9x ARR EX unsynced solo.

I don't see why would you suggest to make old dungeon gear be sold for moogle tomes. All of this is pointless since you can unsync it solo and get it yourself. It's just hard to make old content meaningful since you can unsync it. Most realistic fix is to put astronomy/causality tomes for doing old content.