I'm wondering if since they mentioned Elsa put the Jolly Roger in that bottle without any specific details on how since she can't really shrink stuff if it could lead to a future return of Elsa and the others. I actually heard there might be a spin-off series based on Frozen which I personally would really love so maybe if that happens, it could explain how she got that ship in the bottle.
Adam Horowitz said in an interview they would not return to Once when asked. He thanked Disney for trusting Once's staff with the loan of characters from such a valuable franchise but said their tale as far as the series was done. I think the interview was with TV Line.
I do wish they could bring the actress they had playing Anna on in a different role just change her wig, style of clothing and make up so she wasn't easily recognizable as the same person. Someone with a great sense of humor cause I thought her facial expressions and comedic timing were spot on. The show needs more comic relief, IMHO.
I'd also like to see Disney use her as grown Anna if the ever do a non animated Frozen film.