team victory conditions

[Archonsod]

I strongly dislike the "accidental battles". I should be able to jointly attack a province with an ally of mine without our armies fighting each other.

Surely that should be down to both players to organise, rather than the game? If you don't communicate with your allies, then that's whats going to happen.
I'm kind of 50/50 on the whole alliance thing. On the one hand, it could prove useful to the AI to know that one or more players are working as a team (i.e. it could assess the threat of both players as a combined force rather than individually, and act accordingly).
On the other, your troops are fighting to ensure that you become the one true god. I can't really see them being willing to work alongside these other guys who keep telling them their God is a fraud, and they should worship this other guy...