It would be nice to have a larger array of international trade options. By this, I mean actions like selling horses to another country, or selling a region to another country. In Empire In Arms, regions (controlled minors) and money can be transfer between allies, with your larger array of goods there are a lot more possibilities for buying and selling. Obviously, you wouldn't be able to buy or sell conscripts.
I am Turkey in TGHQ Game 1, and what I would really like to be able to do is buy 'Platoon Fire' or 'Plots and Spies' from France, who is strapped for cash.
I suspect that this type of modification is probably sufficiently complex that you will not be able to implement a change quickly. However, I do hope that you will think about adding this type of ability as you make upgrades to the game.
Thanks