As was noted earlier in this thread, BJ no longer has the skill advantage he used to, so he can no longer defeat the top guys at 170. They're bigger & have the technique to utilize that advantage.
I'd like to see Penn make one last run at lightweight. It was shocking to see how much larger Rory actually was. BJ can still compete with guys like Maynard, Guida, Pettis, Nate Diaz, & Cerrone. He may even be able to beat Bendo. At the very least he'd be a lot more competitive.