It was assumed due to the massive success of Frozen that a sequel would be fast-tracked into theaters. Disney Chairman Alan Horn recently touched on the subject and not only claims that a sequel hasn't even been discussed yet, but he also brought up the subject of a Frozen musical.
Disney is no stranger to Broadway as we have seen stage productions of several films such as Aladdin, The Lion King, Beauty and the Beast, Mary Poppins, The Little Mermaid, and Tarzan. There are even musicals for The Jungle Book and Alice in Wonderland coming before too long. It appears that due to the success of Disney's plays (aka, The Lion King being the seventh longest running stage production in history) it would make sense for Frozen to be expanded in that way.
I personally would rather have a musical done than a sequel. Without expanding on stupid storylines and bringing in unnecessary characters, like kids, I think this would be a good way to interpret the story in a different setting. Walt Disney Imagineers would definitely be able to come up with a cool show to go along with this story. I have seen both The Lion King, Beauty and the Beast, and Aladdin on stage and I must say that Disney knows how to put on a great stage production.
For those of you who don't quite understand what is brought to the table at a Disney stage show, go ahead and check this out from The Lion King.