I understand a happy ending override was inevitable, and I suppose we can go on without Yoda or Anakin/Vader. The problem is Palpatine being dead. He was always the main villain in the saga (even if it was offscreen in the early movies). Continuing past that feels like a post-script season. I can think of a few solutions, but none of them seem easy.
Make Snoke Palpatine. That would take away from Vader’s sacrifice.
Introduce some bigger bad whose in charge of both Snoke and Palpatine. That would feel incredibly contrived and inevitably lead to power creep.
Make Snoke a radically different villain. They don’t seem to be going that way, but at this stage, it’s hard to tell. In the end, the problem with this is that your heroes and villains are pretty set in stone by the whole light side dark side dichotomy. You can make their personalities different, but I can’t see them becoming as diverse as the villains in Batman or Doctor Who.