Famitsu's April issue is reporting that Mario Superstar Baseball (Wii) is set to release June 19th in Japan. If the rumor turns out to be true, that possibly means a North American (and presumably European) release wouldn't be fair behind. The Nintendo Media Summit, being held tomorrow and Friday in North America, will hopefully bring light to some new Mario related titles and release dates.

Link: gamepro.com

UPDATE: Thanks to some new information, the release date has been confirmed for Japan.