I don't think discussion about implants not holding up as expected is insulting. I was kinda shocked by the description used, but it "balls in a sock" is often used to describe the phenomenon of a implant that keeps it's shape in a sagging breast that lost it's breasttissue due to aging (and/or weightloss) and gravity. For the people it is important to know that nothing stays the same for ever, and that the heavier the implant, the more the gravity factor comes into play. So for that it might be a important talk to have, and it might help someone to get a clear perspective on their boobgoals.
As for being insulting to PBD, I'm sure it's not what she wants to hear, but half of the guys say something like: "I still love it", or "It's interesting in a new way". I really feel there's a time to comment on someones look, when someone posts a pic on Instagram and you've got nothing positive to say: Shut up. If someone is discussing the results of plastic surgery (even in the long run), yeah sure you join the conversation. Try to be as polite as you can while still getting the point across.
As to what PBD might think about this? Well she hasn't been online for almost a year, and weather comments on her look have anything to do with that is whole other discussion...