Oooh, an open thread !! Feels so Civ3-ish !
Not sure we'll make a use out of it, but don't hesitate to post here, I might follow you.
As for special rules in Civ4, I personally have none, contrary to Civ3. But if you want to forbid alliances against the other human as well as defensive pacts, that's OK with me. I guess it would lead to unbalanced situations, right ? If you can't think of something else, I'm fine with that.