I don't know if this was suggested before, but one feature that my friends and I would really appreciate is a 'Take Back Request' after finishing one's turn. The new warnings and similar features are really awesome, but once in a while you still form the wrong federation or pursue your plan in the wrong order in a moment of distraction, and this can destroy whole games. If it was possible to ask your opponents if you can take back just your last move, like it is easily possible on the board, this would really improve the game experience for us.
In any case, thank you for this site and keep up the good work! :)