While speaking with ScreenRant actor Chris Hemsworth gave a clue to what he’d like to see in Thor 3. A third film hasn’t been announcement but if the box office is large enough it could help push Marvel into fast tracking another sequel. Chris mentions the idea of bringing Armageddon into the Thor universe. Which I assume he’s referring to Ragnarok that’s brought on by villain Surtur. Odin stole the fire that Surtur needs to light his sword to bring about Ragnarok. That fire just happens to be in Asgard sitting among other important objects in Odin’s vault. It was briefly shown in the original Thor alongside cosmic other items including the Infinity Gauntlet.
“I think what’s good about this is that each time, with the Avengers, we sort of made it difficult to separate them each time there’s some sort of conflict it’s like where’s the rest of the team? And I liked that Thor has another universe or the universe to sort of take care of and keep him occupied. I think that in the comic book the sort of end of days, Armageddon aspect is probably the direction in which it will all head in. Where it’s sort of the end of all things and there’s obviously no script or anything when I read the comic books I thought it was an interesting way to go.”
Tom Hiddleston has mentioned wanting to see Amora The Enchantress brought into the fold for Thor 3. There have been rumors that the Enchantress would be involved with both Thor installments, but that doesn’t seem to be the cast. However, Hemsworth agreed with the idea of having Charlize Theron (Mad Max: Fury Road, Monster, Prometheus) playing Amora when a reporter brought it up a while back. Theron would make an excellent Enchantress but at this point nothing says either will happen. Besides these few quotes from the actors we don’t know anything solid about what could be happening in a third film.