I should've started this discussion a few days ago, but I finally have some time to do it.
With the recent Sun and Moon footage from the last weekend, we now know there will be 7 trials.
Now, remember that promo trailer that can be found in the demo? It revealed several more Trial Captains (or at the very least they appear to look like Trial Captains). They are as follows:
Because we now know there will be 7 Trials and 5 Trial Captains have already been revealed, this means two of them are the remaining Trial Captains and one of them is another Kahuna.
That said, of the three individuals shown in the promo trial, who do you think are the remaining Trial Captains, and which do you think is the Kahuna?
I think both girls are the remaining Trial Captains while the bearded man is the Kahuna. Something about that man just screams
"I've been battling for years, kid." I'm willing to bet he is the Kahuna of the fourth island since he appears in that boat town that is found there. As for the two girls, they don't look as experienced he is, but they look like the kind of people that would give the player a trial to do.
Now for the second question I want to ask everyone (this one might be rather late though; I don't remember if it was discussed already):
What types do you think these trainers will specialize in?
I'm betting the girl with the Mudsdale will specialize in Ground-types. The Pokemon with her already gives a big clue.
For the bearded man, this one was a tough call. He looks like the kind of person that has knowledge about the sea, but we already have a Water-type Trial Captain. I thought Steel-type could fit him because he is found in that boat town, and the boats there are all made from metal. Now, however, I'm thinking he could be the Flying-type Kahuna. The Pelipper is one clue, and his image also looks like someone who comes from the military. Perhaps he has experience with aircrafts, which could fit well for a Flying-type theme. More specifically, maybe he was working for some kind of aircraft carrier in the middle of the ocean? He looks like that kind of guy.
I think the purple-haired girl is either a Ghost-type or a Poison-type Trial Captain. For the Ghost-type possibility, she wears a long dress, which reminds me of sheet-covered ghosts. That same dress is also colored black and has various patches on it, which adds a bit of a spooky factor. Additionally, she has purple-hair, which fits the common color for Ghost-types. As for the Poison-type theory, purple is associated with that type as well. I also noticed her hair resembles that leaked Pokemon from the TCG box about a week ago, and that Pokemon looked like a Poison-type.