This is something we should flag early if we want to do something in time for when it happens: the tenth anniversary of Physics Stack Exchange will happen in three months.
Specifically, the private beta started on 2 November 2010 and the public beta started on 9 November 2010.
Given that everybody who answered the question "where do you see yourself in five years" in 2015 got it massively wrong, I don't think that in-person meetups are appropriate at this time. But maybe we can organize some form of video meetup? Or, failing that, just organizing some tenth-anniversary celebratory swag?