Going to make a prediction based on what I have read on this thread (I don't even go anywhere else for movie info). This is not a spoiler, because it is just my guess, but I am going to spoiler tag it anyways because I've predicted plot points on movies/tv shows before and later been accused of reading spoilers and posting them as my own prediction:
Going off the tweets, I think we are going to be introduced to a new threat, probably from another galaxy. It sounds like they are going to really expand the universe, and the way I see them doing that is bringing in people from "out there" that we have not seen before. Makes me think that Snoke is either - a new character from a planet we have not heard of until now and is invading and trying to take over the planets of the Republic.
OR my other theory is that Snoke knows of an outside threat and believes that what he is doing is the only way to protect and prepare for that outside threat. So he is actually trying to protect everyone from that outside threat by conquering and then unifying and preparing for the upcoming battle. An ends justifies the means type of thing