After binging this whole thread in the past few days, it seems to me that a full-fidelity redfor jet is the thing by far most eagerly awaited, and "we have resolved the legal issues that prevented it" would certainly constitute a milestone.
In fact I'm having a very hard time imagining what else would meet BOTH criteria. The Apache seems to be the second-most wanted aircraft--going by this thread, at least--but I don't see how it would constitute a milestone with one attack helo already available and another well on the way. Also, correct me if I'm wrong, but I think it also doesn't meet the third criteria, that it be something not already announced.
I can think of a couple other things that would qualify as a milestone, but none that I've seen a lot of people clamoring for--drones, for instance, as Kev2go mentioned. And plenty of aircraft that a lot of fans want, but I can't see them as milestones. For instance, with the F-14 already available, what about the F-111 would be a milestone? Or the F-4, for that matter? Unless you broaden the definition of "milestone" until any new aircraft qualifies.
Am I missing something? What else would be "eagerly awaited", "a huge milestone", "brain-melting", and not previously announced?