I’ve been playing through the Lich mythic path, and just got to Midnight Fane. Here I realized that, of the 5 undead companions you can potentially get, only two of them can be had here. I had the impression until now that at least Ciar can be grabbed in Act 3, but after googling a lot, it turns out that, no, you can’t.
With that in mind, I feel like post-Iz is too late to add new companions. This is something I realized all the way back in Baldur’s Gate when one companion (I think it was Alora) could be recruited only in Baldur’s Gate City, one of the last chapters of the game. Almost no one used her as their parties had already been formed.
Now I’m kinda feeling the same way. As a lich I want a fully undead party, but I fell like if I won’t get that until I’m about to take Threshold, it’ll be VERY unfulfilling. I’d suggest providing enough companions earlier to form a full undead party.