*spoilers for THW if you haven't seen it (which I really hope isn't anyone here)*
I just though of what would happen to the characters introduced to the franchise in Race to the Edge after the ending of The Hidden World.
With all the dragons migrating with Toothless some weird stuff could happen...
Wing Maidens: The baby razor whips might just drop them and head off, or possibly drag them away as they fly. Maybe they'd do nothing since baby dragons don't listen to the alpha, who knows?
Defenders of the Wing: Would "The Great Protector" leave? If so, would the entire island be destroyed by the volcano? Would Mala and the gang be doomed?
Beserkers/Outcasts and the like: Their dragons would just... fly off? They can't speak (*cough* RR *cough*) and it would probably distress Heather and Dagur for them to just leave.
Even worse, with all the dragons pretty much flocking to the same area it would be impossible that some dragon hunter/trapper wouldn't notice this and follow... I'm not for a fourth movie, and don't consider these "plot holes" but they are heaps of fun to think about!