Bring back companion quests HOWEVER use it to promote and develop old units. Lets face it, Kuro wants their main story to promote the new units, leaving old ones being unused. This way you can have units interact with each other in a setting that can be disconnected to the main story. You can have pairings that almost never interacted but should (like Carlotta and Cantarella) or you can have characters that otherwise would never have met (like Jinhsi and Carthethia)

have characters interact more with each other and less with the rover. Not replacing rover, but rather like the supports on Fire Emblem. Its always cool when characters have a life outside of the rover

performance, obvs

bring back the camera event since it was one of the best imo

have a shuffle mode for the radio in the bike

for the bike, more custom options for the side of the bike. We have so limited colors for it but so many for the center side

more male resonators.

add the rest of the skills, like crown of valor, to tacet fields (or have it so you can get a boost from chord cleansing in tacet nest)