Trailer Keyblade (Flowing Edge/Lava Slash) candidates:
Hercules: theres a lava and ice titan, but this is water not ice. also, a keyblade would not be based on them if it was a Hercules keyblade and would instead be something more thematic of the film. Plus they wouldn't tease a keyblade for a returning world (especially one already with a keyblade design), which eliminates any previous world in KH.
Atlantis: Underwater city, theres a very short escape sequence where lava is coming up near the end. But a keyblade on this world would based on the Atlantean aesthetic or the steampunk-ish style of the explorers. Not this.
Elemental: Elements water and fire are center stage, but its more so fire than lava. Strong candidate but eliminated based on lava.
Moana: There are both water and lava entities that appear, from the sea and lava. The movie has no other iconography or style or themes to base a keyblade off of. Tattoos would not make for a keyblade.
Conclusion: Its 100% Moana and theres no more debate to be had.
Which in my opinion sucks because skimming through the movie again, there is zero interesting locations or aspects to put in a video game level and explore. Theres a featureless beach, the crabs nondescript cave, and then the remaining 90% of the film is on a raft at sea.
Ignoring a conversation of the quality of the film itself, its more character driven and less spectacle or interesting locale. The Rock will not do the game. From a game design standpoint this is a bad level choice and will be the Arendelle of KH4. But just like Arendelle, it will be in due to marketing/promotional reasons.