SPECULATION Possibility of a whole scene / location we have no clue about?

Yeah, that's one people have been expecting. I think it's possible we get a brief scene in Bast Vader's Castle.

 

I'm with you with Mustafar. I remember reading when Rogue One came out, that they designed the exterior of the castle specifically to match closely with McQuarrie's original design, and that it was built on top of a Sith cave or temple, and that future movies would visit the location. It was not clear if it referred to stand alone movies or the episodic movies, but I remember Lucasfilm clearly stating they wanted to return to this location to expand the canon.

Maybe Kylo is using it as his new crib, or visits to try and commune with Vader. Remember the scene with Vader's helmet in TFA, where Kylo says "Show me again, the power of the darkness...". The word 'again' implies that he has in some way already communed with Vader and been shown the power of the dark side. Whether he actually communed with Vader or was tricked by Snoke (also possible), Kylo believes he has already communed with Vader. If this is the case Mustafar would be a prime candidate for where this could have happened, or would happen again.

 

I agree with those saying that Mustafar is a likely destination that has been kept under wraps. Generally speaking, I think very little of the 2nd act has been shown in trailers -- this includes not just Rose/Finn going to Canto but also Kylo's storyline. I am still holding out hope that we get to see Kylo train as a parallel storyline to Rey training, and that just as Rey learns ancient Jedi lore from Luke, perhaps Kylo learns ancient Sith (or older) lore via Mustafar or Korriban/Moraband.

It would also make sense for him to seek out his grandfather's lair -- e.g. he smashes his vader-like helmet in humiliation, and is looking to claim a more legit part of the legacy.

 

I hope we go to a planet from the prequels instead of a brief appearance from "Coruscant-Lite" ...but seriously though, knowing Rian is actually a fan of the prequel trilogy, I hope we get a glimps of the prequels at least, maybe from actual coruscant since the jedi temple is there and a sith shrine is below it
?

 

I agree with an earlier post that we have seen very little of this movie. I remember when we first saw Rey in snokes throne room and being surprised. If they are willing to show us that, I thought, what are they not showing us?!