I think anyone that thinks Disney can't pull this off is fooling themselves. Think back to Lion King.
Who would have thought Lion King would succeed on Broadway considering that no characters in the movie were human?
Sven's costume could easily be done similar to the costumes in Lion King.
Olaf could be done, but "stage magic" will be needed. I could also see some of the parts where he is split up three different ways probably won't carry over to the stage to well, and probably be eliminated.
I think the biggest challenge is creating the ice castle and etc. I see the use of digital being used extensively. I think it would be the only way to keep the look and feel of the movie. The visual effects are stunning in the movie, I would hate to lose that on stage.
Not to be confused with Dave19.