If it's not a hard thing to change, would you ever think about increasing the limit to like eight players? I was speaking with David (who showed me this game) and we both think that having more players increases the duration of play time since at times playing through with four players can go by pretty quick. Heck we'd even be willing to pay extra for that feature.
Anyway it's just a thought/opinion on how you could make this game even more awesome than it is.
On another note thanks for the awesome game! Ive spent many hours playing the game and making spreadsheets of all their grandslam and tournament results.