Someone to bolster their defensive line with the absence of Vince Wilfork and Tommy Kelly. Standing at 6'4 and weighing around 300 pounds, Ratliff would be at worst a decent run stopper, clogging up the holes that are now seen without Wilfork and Kelly in action.
However, is he truly an option for the Patriots? That answer to me is no, Ratliff for one is actually injured (and may miss the rest of the season) and secondly, his released was basically performance based. Ratliff failed a physical and the Cowboys were tired of putting up with him so they released him. Sure the Patriots have taken gambles on players like him before, but the truth of the matter is simply Ratliff isn't in football shape to play.
The Patriots should definitely explore this option, but I just don't seeing it becoming reality.