Not sure if this has been pointed out, but there was a rumor going around that Mario Tennis: Ultra Smash may have had two extra character not revealed because of the official website pointing out there were 5 new characters coming, instead of 3 that had already been shown off (Rosalina, Toadette, Sprixie).
Turns out, it was just a typo, as you can see when you visit the site-
http://mariotennis.nintendo.com/ultra-smash/play/
-it has been changed back to three in less then 24 hours.
This is probably all we're getting at launch, folks. If there are any new characters they will probably try to milk it as DLC.