A lot of nice ideas here. I think the shirt tearing is important only for what it could mean - the whole episode is about foreshadowing. For instance, they talk about the child drowning while everyone is sitting around a pool drinking, then AJ has people over at the house. It foreshadow's Bianca's daughter doing the same, but like a lot of Sopranos twists, this one never happens. Bobby in the boat talks about DNA evidence, and then leaves it himself. But the greater imagery there is about how Bobby has taken the final step into the deepest sh!t. He whacked the kid and is now a murderer, damned, no way back. And when he comes back to his lake house he grabs his daughter, and sees Janice - already a murderess - hosting to faceless guests. He has defiled his father's "sanctuary." It will always be dark and ruined. His only concern is now his child, who he realizes he has exposed to something horrible through himself and marrying Janice.
Bobby also is the son of the "terminator" who Bobby said always would have preferred to cut hair. The foreshadowing is that Bobby would have preferred never to dive all the way in, but he has, and he can be brutal and evil - more than Tony whom he beat - and he could be the Don. He is more sensitve and child like, but he also can be a monster. Now he is going to become one.
I wouldn't be surprised if Bobby kills Janice to thwart her influence on his kids.