I think Shields could earn a title shot in the UFC with one tuneup fight. I don't know how he'd beat GSP, but then, I didn't know how he was going to beat Hendo either.
I think he would slot in amongst Fitch, Alves and Koscheck, and a match with any of them would be a toss-up. His wrestling would be way too much for Hardy or Daley (who he defeated already, about 18 months ago). The rest of the UFC's welterweights could catch Shields sleeping, but I wouldn't give them more than a 1-in-5 shot. It's almost true already that if you don't have top-notch wrestling you can forget about competing for the UFC's Welterweight title. If Shields joins the party, it'll only get harder.
By the way, if Shields drops back down to 170, he'll be one of the biggest
guys in the division too. Anthony Johnson and Ben Saunders are skyscrapers, relatively speaking (6'2"? 6'3"?), but I think the Strikeforce broadcast had Shields at 6'. I think that gives him a couple of inches over Koscheck, GSP and Alves.