A few more things I'll just throw out there:
Play in warm up mode while waiting for an opponent when hosting online.
Lobby chat from the online menu/match room.
Interactive tutorials/training - I don't mean like space invaders/bowling like VT, just a few things which can point newbies in the right direction and illustrate a lot of the main points mentioned in the documentation with examples in the game (i.e. show an identical shot struck from different parts of the danger zone). I think it may help beginners stick with the game and possibly purchase it.
A quick (optional/skippable) change of ends animation when 3d courts are enabled - would show the surroundings a bit more, when using the default camera you don't see much of the stadium.
I don't know how easy any of the above would be to implement, or if they would be worthwhile and I'm not complaining about not having them, just offering some constructive advice