I've been experimenting with a single racetype-specific Champion for each faction which acts as a "sub-sovereign" and is very difficult to kill. This is to offset a corresponding increase in monster difficulty that I am also working on, since for now every AI champion is a walking collection of injuries by the time I encounter them. Anyway I want to force the first champion of each player and AI faction to come from a defined set, after which the mechanism should work as normal. What I've found so far is that the <Prereq> tag is totally ignored for champion selection, but maybe there's some other way? For sure Kingdom/Empire champions don't mix, at least.

Separate, related question: Does AI understand the Iru Elixir is and what it's good for? It seems like even late-game champions have an embarrassing list of maladies, which makes some of them very easy to roll over.