Personally I would overhaul the trust system bigtime (not the MSQ trust, just the free-team mode).
Right now trusts are very limited and locked into their associated expansion and the leveling of them seems near pointless (unless you really want to bring trust X into this dungeon they weren't in before.
Instead I would make a new system where any unlocked trust could be brought into any unlocked dungeon that supports trusts. And instead of grinding levels (they stay synced with your level) you will grind rank for them.
For example with Urianger, he starts at rank 1 and when he gets to rank 2 he can use Earthly Star, rank 4 might be Royal Road, rank 7 could be Spread, rank 9 might lower the cooldown of his Death spell, while rank 10 would be an outfit.
And you're not limited to just the story NPCs, but can unlock a lot of different NPCs from the game, each with their own unlock requirements. Hien could require to complete the Doman restoration, and at rank 10 you unlock his LB3 as a glamour for your SAM.
Some trusts would also have synergies, such as the twins, or perhaps Lyna having synergy with a melee DPS for bonuses. They would also have different LBs (like alisaie's LB2) and temperaments with them. Plus personality would play in how they behave, so Hamon Holifist might be a bit slow to dodge, or Dorgono will ignore AoEs if she's in frenzy.
All this could make it more fun to rank up each trust and have them useable across all content instead of being tied to each expansion. Make your dream team and bring them to any dungeon you want. For lore reason (like how Hien is with your in Satasha), call it rememberance mode and you have your own "what if?".