This may be more of a topic for online games, but it also could apply to games vs. the CPU. What do you think about adding an option to have a brief warm-up prior to a match, where each player could hit a few feeds from the opponent (practicing volley, smash, etc.) and also practice serving? This would be like real tennis matches are played. I think that it would be neat. Maybe this would not be available if using the demo unless one of the player's has the full version, due to the time limit in the demo-only matches. This could also be done having the CPU take over the opponent's character for this warm-up session, and each player's warm-up could be shown in a split-screen prior to the match; this way, the CPU would be sure to hit the proper strikes for warm-up (shots for volley, lob, etc.), and it would take less time as each player could be doing the warm-up at the same time.
A similar request is for the addition of some training games, similar to what games like VirtuaTennis have. At least, could we have an aiming helper for practicing the serve that would not work in matches, but it would help us to see where a serve would be positioned prior to hitting it.