The ending of the second movie with Uma saying ‘It’s not the end of the story’ makes me think 2 things:
1. There’s gotta be a third movie (fingers crossed)
2. Uma’s gotta make a come back
So I’m thinking that the VKs will be fighting an opponent and that opponent is totally dominating. The VKs retreat but find themselves cornered by some body of water(ocean, probably). Right then, the waves wipe out most of the opponent’s henchmen, and when the waves settle, Uma is standing there like “I’m baaaaaaaaack” (yo and she could sing poor unfortunate souls, bc the first verse would be totally relevant). And if Uma comes back, Harry and Gil better make an appearance, or at least a mention. Maybe Ben finally brought all of the Isle kids to Auradon.
Another thing I would like to see from the next movie is seeing a good kid go bad. That’s the one thing they haven’t explored. Also, Ben would have to deploy Auradon forces bc its a domestic issue (and Ben is always the damsel in distress, maybe he’s a tad salty). Of course, Mal and the VKs would ultimately save the day. Because the antagonist committed crimes against the kingdom, Ben would be forced to send them to the Isle. He might be troubled by it, but he’d have no choice.
I wanna hear other theories! let me know what you guys want to see :)