Since every other prognosticator has failed in pinpointing a date for the release of Pope Benedict XVI's Motu Proprio granting more freedom to celebrate the 'Tridentine' Mass using the Missal of 1962, I figured I'd joined them.
My picks are:
April 30 - Memorial, Current Liturgical Calendar
May 5 - Feast Day, Previous Calendar
July 14 - Quo Primum, the promulgation of the Tridentine Mass