We still don't have a precise start date for PS Classics support on PlayStation Vita. But we do have something a bit more specific -- a firmware version number.
Sony said today that PS Classics support will be added to Vita via the system's version 1.8 firmware update. As previously announced, this firmware update will be available some time during the Summer.
The version 1.8 firmware update was mentioned during Sony's announcement of the PlayStation 2 Game Archives service for PlayStation 3.