Who cares? Silva is not a threat to GSP's legacy, he is a middleweight. Hendricks is banging on GSP's door right now, saying 'Oi, I smashed everyone else, you're next!'.
GSP claims to care about legacy... to leave 170lb now would do it damage IMO. He's not like Anderson, who has already made a point of shifting weight class without needing a superfight as motivation.
GSP is the 170lb division. I don't like to say it but, my initial reaction if he fights Anderson instead of Hendricks is that he's sold out.