I frequently change into a pajama top at my seat, especially when in an odd-numbered window Polaris seat (which are a little more private than most others). I'm male, so worst case someone walking past sees a little bit of topless skin - not exactly a good business-class look, but hardly an issue on either side.

I don't use the pajama bottoms, but I do change into shorts during boarding (and back before landing). I wouldn't consider doing this at my seat - especially as I change during boarding when there are people everywhere. However I don't disagree that if you were to take suitable precautions (such as covering up with a blanket) and do it at a quiter time then I can't see any real issue with doing it at your seat.