Developers interest is not in that direction, secondly this game mode won´t support coin-games due to USA gambling laws or something like that. Although yeah, it seems there is heck of interest, same supports uservoice:
https://warlight.uservoice.com/forums/77051-warlight-features/suggestions/1088481-peace-treaties - top voted idea.
Not to disappoint you, but it seems its never going to happen.