I see no problem in OUAT incorporating these characters into the show and enjoy the backstory and added character development it has given them. Since Frozen is sure to be a classic Disney film long into the future, I think the cameos of minor characters and new storylines are a good direction for the show.
Yea sure I like the idea. I really enjoy the show Once upon a time and its use of fairytales. Just because Frozen is relatively new does not mean that it should not be used. I am also really excited for my daughter to get to watch it with me and see real life frozen.
I haven't started watching Once Upon a Time yet, but it is on my list. I am definitely interested in seeing where they go with the Frozen characters in the show. I think it plays in to the show well, since it is based on fairy tale characters and their lives.
Since Frozen was a hugely popular film, it's a great move by the producers of Once Upon a Time to bring in the characters from the film. The likelihood of its following increasing is pretty high since the movie was loved by so many people around the world. It has the ability to grow its audience and get better ratings in their Sunday night timeslot.
As the parent of a not young girl I have not seen Frozen and I don't really intend to. Given that Once Upon a Time is crossing over characters I have to assume I won't see it either. I'm not a fan of these movies and I think there popularity is due to over marketing, not genuine interest.