I can't find the link where I read it, but you are probably right. Maybe Hulk helps Asgard to stop Surtur from triggering Ragnarok?
But you know, we all think of Ragnarok as an event, but with no plot leak yet, what if Ragnarok is a character and tied in with the Sokovia Accords (he was a cyborg clone of Thor via Tony Stark in the comics) on Iron Man's side? Now that's interesting...
Read this:
https://en.wikipedia.org/wiki/Ragnarok_%28comics%29
It seems like it would fit pretty nicely into the overall storyline. So, Thor will wrap up the Civil War mini-story and re-unite the Avengers for the Infinity War story.
You heard it here first.