Few points I'd like to discuss or have cleared up if I'm incorrect about the ideas I'm getting.
Firstly, One thing I'm curious about is if we battle the Trial Captains or not. As they're given type specialties in the trailer and main website, I'm pretty confident that they will be battleable at some point (Probably Post-game) yet the information seems to suggest a battle against them isn't part of the trial.
So at the moment I'm assuming the layout of the trials are:
Meet Trial Captain > Complete Trial > Report back to Trial Captain > ?Battle Trial Captain? > Battle Totem Pokemon > Repeat these steps until all Trials on island have been finished > Battle Island Kahuna > Move onto next island and repeat.
The bold text is indicative of the one stage of this formula I'm not quite sure whether we'll be doing or not.
Second, the idea of Sun and Moon being a less linear and more open game has been discussed since we discovered the region was based on Hawaii and is going to consist of multiple islands.
With the reveal of the Island Challenge as the main goal and objective of the game, I'm starting to find this more likely. I think (Or perhaps hope would be more accurate) that the various Trials on each island can be done in any order the player wishes, whereas the Kahuna is always the final challenge of the island.
Third, Has there been any word on how many Trial Captains there are? Seeing as GameFreak seem to be breaking away from the Gym Formula, I hope they go all the way and don't just give us eight Trial Captains and Four Kahunas, basically another Pokemon league scenario. Is one Trial Captain for each type too much to ask for? Or a least let us have a Dark specialist Trial Captain. Please GameFreak?
Lastly, overall the games nowadays seem to be getting easier and easier, I hope the trials offer a decent challenge and I'm really hoping the Kahunas are truly fiendish boss battles. As the final trial of each island, they represent the final challenge of each act of the story and Hala's pre-battle screen looks particularly epic, I'm really hoping GameFreak doesn't pull their punches with these bosses for once.