Just do V again with a different story but add some returning characters and I'll be happy. Of course, some things could be tweaked, like less loading and less frequent random encounters (or ditching them altogether).
Of course, I wanna see what strategic battle they can come up with (II's is still my fav). I'd love to see cooking contests back in some fashion, as well as the theater from III.
But in general, I want them to ditch the battle system of Tierkreis and use again V's one, or even III's one, those two are the system the series should use