@jwildeboer When the Social WG discussed about the protocol, I provided commentary. At that point in time, I already had worked with the Diaspora protocol and knew their way of distributing comments. I'm not totally sure anymore, but I can imagine that I suggested that to the WG as well.
But I guess that AP inherited their current behaviour from pump.io. Sadly also LD signatures didn't took of. So we would need a different method of authenticating especially non public posts.