It looks like the next Tales game may indeed be "TOZ." After seeing a bunch of Tales of Z... trademarks in Japan, and having one of them also make the European trademarks, it seems that Tales of Zestiria has also now been trademarked in the U.S. as well.
And again, casual reminder that this does not exactly set in stone that the next Tales game will be this, nor does it mean said game will be making it to the West... But it seems they are definitely leaning toward the probability of doing so. Whatever the next Tales game will be, it seems that they're leaning toward "TOZ."