At the moment, most fans seem focused on the rumors about the relation between Elsa and Anna. If it turns out to be true that the two are not related, this could have some interesting implications on the plot of the film.
It would be interesting to see how the writers incorporate this into the story if it is true though, as it should have a specific purpose in the development of the plot. Fans have been trying to guess what that might be, but to no avail so far.
Could we see a crossover with another franchise by Disney? It’s not very likely, as they would probably want to keep their focus firmly on “Frozen 2” right now, but it’s maybe not out of the question for the future, perhaps after the release of the next film. If that really is planned, we would expect Disney to start hyping up their fans well in advance.
The studio already tried exploring more interesting territory with “Frozen” with the special musical that they released previously, so anything is possible right now. The best course of action for fans of the original “Frozen” would be to focus on the news we’re getting about “Frozen 2” at the moment and discuss the things we know are facts, instead of getting too carried away following the various rumors that pop up on a regular basis.