JPGames.de was able to have a talk with Tales of Series producer Hideo Baba in Munich, Germany. The full interview from them isn't out yet, but here is what Baba-san said regarding the recent Tales of Symphonia HD remaster rumor.
Baba-san also adds: "We can’t really say anything before announcements are made and it’s always a bit surprising when people ask us about rumors like that. It would be best to just wait for new information [about Tales of Symphonia’s 10th anniversary]. Before we announce something, a rumor is just a rumor after all (laughs)."
All we can really do as of now is just wait and see, I guess.