I know it is a small thing, but I would guess it is a simple thing to add.
I am not sure if anyone suggested it, but it would be very convenient to have an alert when it is your turn.
I have played multiplayer in windowed mode and was browsing at the same time. What happened was that we made each other wait, a lot. I simply could not hear the very light and quiet sound when it is your turn.
It can be added to options to be turned off/on, some sort of loud and clearly visible alert.