Imo, this is still the best theory about Capitano's return

The best theory is that, if Capitano does come back, it won't be the "original" one, but one that has the soul of Capitano/Thrain based on the tales that were written about him in Natlan. In the AQ we've seen the soul of Guthred, but it was not the original one, it was a soul of a different version of Guthred, created by the stories about him. [We know that both souls can coexist at the same time: in fact, we have also seen the real Guthred in 5.1 AQ] That "diffent soul" concept was ony used there and no where else and it would be strange to introduce it without a real way of using it. So the best way to use it is to create a new soul for Capitano. We know that our man was a legendary hero and that there are many tales about him. There are also new tales that are being written after the AQ. So the new Capitano soul could have both the knowledge of his past as Thrain and his "present" as Capitano. Maybe the Lord of the Night herself could give him all the memories of the real Capitano, so it would be a perfect "replica". This could also solve the problem of Capitano's (real) soul being merged with the Lord of the Night and "sharing" the curse with her.

The new soul could either: 1) possess Capitano's old body 2) get a new body, maybe created by the LotN or Capitano himself 3) get his old aspect as Thrain

I don't know / I don't think other fatuis will be involved in his resurrection... If we also consider this possibility, maybe (and I say maybe because it's very unlikely) Dottore could create a puppet for the soul to possess.