Philip Hodgetts thinks it will be June 21st, though it seems this is based on when "Spring" ends:
In Feb, invitees got told "Spring". At NAB they said "June". The latest it can be is June 21..]
I've been trying to decide whether Apple will release - or even show - Final Cut Pro X at the World Wide Developers Conference next week. I'm starting to think that they may do neither; it's not like the World Wide Developers Conference is a huge video editors event. It just seems the wrong location to roll it out. Which suggests that they may roll it out a week or two after the WWDC at the earliest.
There's one exception to that prediction; if there's something they haven't told us about it...some tight integration existed with either Lion, iOS or iCloud - or all three. If you can seamlessly work with content on iCloud, that might provide a compelling reason for going "and by the way, here's the update to our video editing application" during the keynote. They might show it.
But face it; with a new OS, new iOS, and iCloud to cover, any reference to Final Cut Pro X is going to be less than five minutes; otherwise the keynote is going to last the best part of a day.
Of course, I also predicted that Apple wouldn't show or announce an update to Final Cut Pro at NAB. On a technicality, I was right - they didn't demo or announce it at the NAB show - but in reality, I couldn't have been more wrong.