Chrom or Shulk would be a much better pick for TGS tbh, Isaac isn't as popular as either of them over there.He might not get revealed before release, though. Actually, Isaac might be a good character to announce at TGS (if Nintendo will even be there) since he's quite a popular pick in Japan. It'd be fitting, really. One really popular western AT promoted to playable, then another really popular eastern AT promoted to playable. (Here's hoping.)
If you're getting the idea that Isaac is extremely popular in Japan from the thread title I had up a little while ago, that was due to GS's surprisingly good placement on the VC sales chart there, not due to his Smash demand, which has steadily decreased in the east since the Brawl era.
I mean he was popular there at one point, so people would still enjoy seeing him, but if Sakurai wants to pander to a Japanese audience, there are better characters to pick.