The issue of the vague hint text is really thorny to me, because a lot of the fun for me in games like this comes from experimenting and figuring out how best to deal with different threats. I know I had a lot of fun with them on my playthrough of Arcade's story mode. Maybe if you die a lot to a specific threat, it could give a slightly clearer hint on the death screen? Some names for the ability coins would also be nice, though they certainly don't have to tell you everything. Just something that lets you tell them apart without having to squint at the pictures.
As far as the CUSTOM part of Arcade goes, it'd be really nice to have some preset challenges to help sort of work your way up to Max Mode, but I get the feeling that's already in the works. Gallery updates would also be nice.
also arcade maddie when. misty got 3 forms and she isn't even IN nightclub anymore. arcade kass would also be fun especially if she's actually sort of on your side to some degree, maybe using that mythical Player 2 slot...perhaps with the caveat that if she catches wind of you using Saya's powers she becomes a threat? shrug at this point I'm just spitballing about stuff you probably have planned anyway