Can't believe I'm agreeing with something v3xi said, but GSP did say awhile ago if he was going to fight above his class he would need time to properly put weight on. I think Silva has two purposes here. One setting up a higher payday, and two giving GSP time to put his weight on the way he wants. The only fight I see Silva taking in MW is possibly Bisping easy and good sales.
I'm also for fight by April or a interim belt is fought for, and still not fought for by September he's stripped and the interim is now the real belt.