As much as I absolutely love Frozen, I wouldn't do it. On our Epcot day in February, we stood in the Norway gift shop just long enough to get a peek a the girls, and that was good enough for all of us.
Me, being a child of Fastpass- meaning that I can't remember a trip where we didn't use fastpass. I remember being 7/8 years old and being the "runner" for the Legacy FP. Hence, I get antsy waiting in a line for longer than 30 minutes. The same day we peeked in at Anna&Elsa, it was a big decision on whether I wanted to get in like at 1:05 for the 1:45 Aladdin and Jasmine m&g- which was 30 minutes. I couldn't imagine standing in line for even twice that.
Another thing- I'm always afraid of the really lame interaction. On our last November trip, at the time, Rapunzel was my favorite Princess. We made sure to get a fastpass for her, and I was ecstatic to meet her. I got in and began talking to her, and she just didn't seem very Rapunzel. Then, at the end, just like I had been doing with other characters, I went to take a silly selfie with her. I said "Let's make funny faces" and she said "Well you can do that, I'm going to smile" and I was a bit disappointed. If I met Elsa and Anna, I wouldn't want to get hyped up to take a cool selfie, then be shot down.