I'm hoping that NPCs like Minthara or Halsin or Sazza are the actual model for non-companions and how they will be introduced in the game. The way Lae'zel and Shadowheart are introduced in the prologue and then right at the beginning on the beach seems reasonably well done, a couple interactions. Wylls introduction at the gate is kind of camp, but brings him into the storyline. Gale and Astarion I think both feel a bit forced in the way they are introduced. The way the dialogue is written and how the cinematics play out, Gale and Astarion could both come into the story later I think, rather than immediately.
I'm guess a Ranger companion will materialize, since its the only class currently available for the PC but that doesn't have a companion yet. Halfling might work for that, though I'd like to see a human female for balance since we already have Gale and Wyll as humans.
Minthara would be a good alt for Shadowheart, both elves-ish and clerics, especially if Minthara was more STR/Con oriented for heavier armors and tank up battlepriestess mode, so its not just a rehash of Viconia from BG1/2.