About the GPT-Dealbreaker exploit (Trade gold for GPT, then declare war), I'd like to include resources too. Kinda a semantics issue, but it's good to remind people about that (and avoid misinterpretations).
Also, It'd be good to have a rough turn limit on that, or some conditions that allow someone to break this deal. For example, the AIs settling right in your face when their capitals are on another landmass. Maybe you'd be able to break the deal after, say, 15 turns and only if you have a casus belli?