[Endoperez]

Would it be possible to make a line of provinces in which dominion of spesific strength would spread at spesific rate? Like, the player would have one immobile H1 priest in one end (only good for preaching), and the AI would have a temple in the other end, and the enemy dominion would spread into the only direction it could and thus set a time-limit for the gauntlet.

If so wanted, the player's prophet can be pre-defined and set to be an immobile in a separate province with 0 population, surrounded by enemy temples. That way, the player can't appoint a prophet.
Similarly, there could be 15 independent heroes with as much experience as desired to keep the gauntlet heroes from getting heroic abilities instantly. Perhaps one with 25, one with 50, one with 75 and the rest with 100 experience, making the first heroic ability pretty easy to get and the others progressively harder.

Being able to recruit independents would affect the outcome too much, in my opinion, especially if the poptypes were random. There's at least one poptype which has only two recruitables (Commander, Slinger); changing commander and slinger into something that would be recruitable everywhere would be nice.

Player's nation's settings should be defined in the map file, to ensure that everyone gets the same amount of money and resources. There shouldn't be any dominion in the gauntlet area at all, because it would affect morale.

It would probably be quite simple to give each nation different set of starting units. One starting province per nation, starting units replaced with e.g. Black Lord and Master Smith and an arbalestman-made-commander, and 0 pop (and high PD?) to make taking the capitals of other nations worthless. The actual gauntlet could be the same for every nation.