PlayStation LifeStyle found mention of the patch (v3.01) on a french gaming website. All indicators point to the April 16th release date. However, PSLS has more information about the separate, and later, release date of the voice-control patch.
( SingStar Vol. 3 , PS3, SingStar , SingStar ABBA, SingStar Amped , Singstar Hottest Hits, Singstar Queen, SingStar Vol 4, Singstar: Disney, Singstar: Hits From the Musicals, SingStar: Pop Edition, SingStar: Vol. 2)
Tipsed by: StalkingSilence