Oddly enough, the more I think of it, the more I wouldn’t mind if Snoke was Plagueis. It’s a prequelism, but one could easily look past that. It’s not hard to believe that the Emperor would have a master. If midiclorians are discussed, ew, but I doubt they’d do that. If its revealed he’s the real puppet master behind Palpatine all along, ew, but it could easily be that Palps wounded him (in a murder attempt) and he’s been hiding since, waiting for his chance or something like that.

Retconning the PT is not an issue, as Palpatine could have been lying easily or might not even had known he was dead. Overwriting the EU is not an issue.

The reason why I’d be okay with it is because realistically who is Snoke? If he’s supposed to be the new big bad, he sort of needs to be at least on the same level as Palpatine for him to seem an imposing villain and the ultimate evil of the trilogy. So, if he’s on the same level as Palpatine (and has all this dark side knowledge) where did he come from? That he was the Sith lord who trained Palpatine is as good an explanation as any, and the fact that he’s already been established helps reduce the random factor (some might say there should be a random factor, but to me if this big huge bad is just some rando dude that came out of nowhere it doesn’t feel quite right, when you look at the saga as a whole).

For the record though I’d say he most likely is not Plagueis.