Lol, so much reaction to this ch. I don't think Bach meant that Ichigo is literally his son. Probably referring to something else.
This is my speculation:
I am thinking Isshin was a Shiba, maybe head of the clan, and fell in love with Masaki who was a Quincy that is related to Bach somehow. Therefore, Ichigo has Shinigami blood and Quincy blood. This explains how people in SS don't recognize the name "Kurosaki" since it might be a made up name or was Misaki's name and Isshin took it. Ichigo resembles Kaien since they are related. Well, just my thoughts, not saying that it is fact.
Aizen doing something to Bach, how did he do that when he is supposed to be sealed? I guess that is why Aizen is a war potential.