I do remember before 3.x hit the shelves, this support forum had it running for a couple of weeks or so beforehand. I imagine what you say is more likely. A public beta, an ipb community run and then public release.
Back in the day, I remember one of the big things about ipb 4.0 was that of detaching it from the core. Meaning that blogs, IP.content ect can be installed as sepeterate instances. Is this still the case?
With the projected release Q2 of 2014, when is ipb 4.0 due for release? If close, it will be time for a licence renewal as detachment is something I really am looking forward to!