The thing is though, Surtur is going to be CGI, and so VERY expensive to use, just as the Hulk was used carefully in Avengers for that reason. So that might be a reason to not center an entire movie around him showing him A LOT. Instead they may hint at him through much of the movie, maybe give us a few glimpses, maybe a few obscured shots as he's making his sword, building anticipation and then BAM! a big confrontation at the end. You have to think about it from a filmmaking/storytelling standpoint. This actually makes sense. plus we'd have the bonus of being able to see others of Thor's "Rogues Gallery" in Thor 3, assuming we'll get one. Also I recall Feige and Branagh mentioning that they are very cautious about sequels, and it all depends on how the next one does, I think Tom or Jaimie said that also recently about a Thor 3, SO, with that in mind they probably wouldn't tease Surtur for a Thor 3, because what if Thor 2 bombs and they never get to a Thor 3? (NOT going to happen, but I'm just saying, that's what their thinking is as businessmen...) Also, in order for it to flow with the rest of the MCU, whatever happens has to be basically resolved by the end of Thor 2 (not necessarily meaning we won't see Surtur again, understand, but this particular confrontation would need resolution). So you can't for instance, have Surtur invade Asgard and cliffhanger that for Thor 3. As for wasting him, well there really is quite a bit of time left based on the scene numbers (in comparison to Thor 1 and Avengers). plus I'm expecting Thor 2 can be at least 10 minutes longer than Thor 1 was, based on running times of the other films. So there really does look like there is plenty of time for them to bring Surtur to London and then even take the fight up to Asgard and resolve it there. It could work.