This is based upon the "missing" sprites, the currently released trial captains and kahunas, the current totems, and the number of UB's.

It seems from early access reviews, the game will have seven Trials. This seems to make sense from the footage we've seen and missing sprites.

If we take the assumption that Wishiwashi School Form is a totem Pokemon (which is the only stretch to make here), then we have:

Ilima: Normal/Gumshoos/Raticate
Mallow:
Grass/Lurantis
???: Dragon/Hakamo-o or Kommo-o (probably the former)
Sophocles: Vikavolt
Kiawe: Salandit evo
Lana: Wishiwashi school
Ghost/fairy girl: Mimikyu

The only major stretch being Wishiwashi. It further makes sense considering the Kahuna types revealed, being:

Hala: Fighting
Olivia: Rock

And from the trailer, I'd assume the bonnet-girl and the bearded man are also kahunas, with ground and flying types respectively.

That's 11 types. There are seven remaining.

Wouldn't it be cool if there happened to be seven things to take up the remaining types?

There are: UB's. If all UB's take up one number with the exception of the UB-02 pair, they could theoretically fill out the remaining types:

Bug (likely the 02 pair)
Psychic
Fairy/ghost, whatever isn't the trial
Ice
Dark
Steel
Poison

Thoughts?