All right, I've gone around and grabbed some information about Ys: Celceta, Sea of Trees from the importers who have posted about it.
-It's not as big as Ys Seven, play-length wise- it's about a 20-30 hour game.
-All characters have some kind of environment-specific ability (the game uses a version of Ys Seven's party system). While Adol's only environment action at the start is accessing memory fragments, he supposedly gets another one on top of that.
-Believe it or not, it has in-game rewards related to map-completion %, as Adol and his friends are also tasked with mapping the uncharted depths of the Celcetan forest.
-Unlike Falcom's previous remakes (Ys Complete/Chronicles, Oath in Felghana), this one will have very few remixes of tracks from previous versions of the game- only five of the game's tracks are remixes of works from prior installments of Ys IV.
-Unlike all prior installments of Ys IV, there are no segments of the game that take place on the island of Esteria. This is a fairly large story change, as at least a couple of characters from Ys I & II ended up getting heavily involved in either version of Ys IV, and those characters not being present does change things a great deal.
-Also, as many of the memory fragments will contain bits of Adol's pre-adventuring life, Falcom is giving us kid Adol- and showing us that he's not the only person in the setting with red hair.