A quick update on my previous post: without mentioning the exact countries, I received several tips that NDA press invitations have been already sent out for an event scheduled for next week. The official announcements are usually few days after those closed doors press events.
In another country, Nikon reps are already scheduling in-store demos for a new camera.
Everything so far points to a major product announcement, most likely the rumored D800s camera (and not Coolpix cameras). The D9300 is also a remote possibility, but I have not heard any rumors on that model since April.
I still have no exact date, but I am guessing the official announcement will be in the second half of June - just like I reported it last month.