It's cause they are ashamed of Little Mermaid and Tarzan. They would have made room if the shows ended up being hits. They even had time to announce Frozen was coming to Broadway. Just cause it made the most money out of any Disney animated musical, doesn't mean it lends itself nicely to the stage (which it doesn't in my opinion).Can you imagine if it bombs?
Hopefully long. Disney sucks when they try to fast-track productions. I have a feeling this Frozen show is going to be rushed. I doubt they are going to take it out of town. The show doesn't lend itself to the stage all that well. Its not really a Broadway musical type of film.
I think they will probably have a tryout because every single Disney show to date (aside from Tazan...) has had one (with Hunchback, Aida, and Aladdin having 2)