I'd happily trade K for I&A in camp.
Maybe formally make K a camp caster, unable to trust himself to leave camp (and would be attacked on sight outside of camp anyway).
His training could also aid in rolls to attempt domination of the Elder brain.
Who is the I in I&A? I assume A is Astarion?
I did a bit of thinking about Ketheric joining camp:
I would see Ketheric in camp a bit like Loghain in DAO. Yes, he probably has a lot of interesting stuff to say - Loghains insight during Return to Ostagar was pretty good, especially if you also take Wynne, who can ask some questions, the pc can't ask, because they weren't there as long as she was. Minthara could be the Wynne of this situation. On the other hand, I really can't see that working. There are five people (if you recruit everyone possible) in camp, that would be very likely to attack Ketheric for what he has put them through: Aylin, Jaheira, Halsin, Minthra and Isobel. Though Isobel might be able to forgive her father.
I guess, if Larian had implemented to Ketheric as camp follower narrative, then you probably would have gotten some downside aka DAO (where you loose Alistair, who might at that point be your designated tank). In this case, you might loose one or more of the above mentioned characters. I really can't see Jaheira, Halsin or Aylin forgiving Ketheric and work with him. Isobel and Minthara might be.
I think, Ketheric would have made sense in an evil playthrough, maybe instead of Aylin. Since they teased more stuff for evil playthroughs with patch 7 and right now, you loose a lot , if you go full evil. Ketheric could bring Z'rell and Balthasar along maybe to make up for the loss of Wyll and Karlach.
But that is just speculation. I really doubt, there will be more companions for evil playthroughs tbh at this point. This is more, how I think, it could have been implemented from the start.