I don't mind the Trusts for the trials. Makes for an more involved fight.
There are just two things I want them to pay attention though when doing it.

First:
Make it more plausible in the story. At least for the second trial it felt forced how all the characters were there. I think the leadup to the first trial was far better.
At points it really felt that they wrote the story around the trust system and I think that limits them in creativity.
Make it so more characters can be trusts.
Zarool Ja and Koana were great. Why not have Bagool JaJa or Otis as well? The scions sometimes seem only to be there to fill the Trusts.

Second:
Keep the final trial free from them.
This is just my opinion and nothing more but I like how we take the center stage in the final fight of an expansion. Stuff like in Endsinger is ok but I think the final fight should be the time for the WoL to shine. It is the great finale of an expansion.