I also think it would have been a neat way to connect the trilogies, but i trust in Lawrence Kasdan to have created a unique new character. What we know about Snoke that he dates back to before the Clone Wars, so he's old. I don't mind if he a new character at all, as long as he's interesting and they can make him work.
The things is don't take this as 100% official, that it's not Plaguies. J.J said numerous times that Benedict Cumberbatch did not play Khan in Star Trek into the Darkness. Do i think it's likely at this moment that he's Plaguies? no. The thing is Star Wars is a big universe , why make it smaller? by including old characters. There are so many other force users out there, light and dark who are neither Jedi or Sith.