If you want a villainous speedster with a mysterious identity and a connection to Barry Allen, then Harrison Wells is your man. Because he spent Season 1 of The Flash doing exactly that. Tom Cavanagh is going to be a regular on the show once again this year, although it's still not clear how that will work, so could he be Zoom? It's likely that the Wells who is still alive in this universe will exist on Earth-2 or some other alternate dimension, which is where Zoom is set to be coming from, so that's at least one tick in the box. And if one version of the character has already targeted Barry and been a villainous speedster, then there's a chance it could happen with another. The biggest sticking point for this is the fact that it just seems like too much of a repetition of the first season. Because it would be. On the other hand, though, Wells made for an extremely compelling character, and having him perform a similar sort of dual role would be understandable given Cavanagh's performance. Plus, it's so obvious that you just wouldn't see it coming.