Well, given that the PS4 isn't even out in Japan... it's a valid decision.
It's not like Tales games are pushing the graphical limit anyway.
(Kinda why I hope they stick to cel-shading)
EDIT: I think it still may be Vesperia related. Between the book, the "tov" in the web code, that back in 2009 (yeah, I know, don't say it) Namdai said they'd be interested in a Vesp sequel, and it'd save money in the resource department.
But maybe it's a Phantasia-to-Symphonia kind of sequel
EDIT II: http://gallery.abyssalchronicles.com/displayimage.php?pos=-18106
Translation of the now open book by the fan community.