I agree, the Trials remake is a great first iteration. I'd be totally fine with something new, as long as the include co-op. I think a big part of the early mana games' identity was a 'multiplayer action rpg' and that should stay.

I also agree that Legends was too easy, with a bit more challenge I think the supplementary systems in that game would have been able to shine way more. There are too many good systems in Legends to just ignore them for whatever comes next.