I really miss a cancel button when the game is exporting, for small games it's not a problem, but for a large game it takes a while and sometimes you forgot something and would be great to have a cancel button while the game is exporting.
Another thing it would be good is a option to export only the js runtime file, like if you make a minor modification on the game logic and don't need to export all sprites again... it would accelerate the game developing a lot!