At this point, it wouldn't hurt to at least shake up the formula of dungeons in FFXIV. 3 bosses separated by trash gets boring.
I always think leveling dungeon are the best because missing parts of your kit make things more complex in a sense. There used to be that one dungeon in expansions I have a love-hate relationship because of this (The Vault, Doma Castle, and to a lesser extent Holminster) it's just so much harder in comparison to max level dungeons that we are used to simply speedrun with no thoughts (I guess because max level makes us so powerful, and synch down is alway in our favour).
I'd keep the leveling dungeons mostly as they are, but max level dungeons could do with more depth in either mechanics or design. What about 5 bosses rush and no trash? Massive amounts of mobs that we should find a route through? Environment mechanics (more than "don't stand in that" like Aurum Vale).
And a real hard mode (without being a WoW Mythic+ copy) could be interesting. It shouldn't necesserally provide raid-level gear, but more tomes and a few cosmetic rewards would work just fine.