CatBus said:

The contention is that he is an existing character from the prequel films, and the revelation of his identity will shock viewers.

Presumably, his identity would be already known enough to viewers to shock them when it's revealed. So either it's a presumed-dead-but-actually-not PT character, or a presumed-irrelevant-but-actually-not PT character, but the only guarantee is that, if this is the case, disappointment will overwhelm any shock felt.

If that were the case then my two main suspects would be either Sifo-Dyas or Plagueis. If it were Plagueis they could be working up to explaining Shmi's unexplained pregnancy.

Though if they were either of those then there's the big question as to how Han and Leia's daughter ended up with such a character.

But I really hope that particular bit of info is just wrong in the end. I really don't want any PT in my ST.