I don't know if these ideas have been suggested before, but I have two ideas:
1. I'd like to be able to reply to an opponent's message after I've moved. I just recently completely forgot to respond and now I feel bad. It would be nice to be able to hop back into the game after I've moved and add a response.
2. During games where there's a lot of chatter and large messages being sent back and forth, I'd like to be able to resize the chat window so I can see my whole message. You can resize it now, but the text-box stays the same size.