Would Google buy Square? I doubt Google really wants to get into the offline payment market. If Google really want to fight Paypal as alternative online payment platform, it would be better for Google to buy Stripe.
Apple and Amazon are other potential suitors for Square, but the company is kicking so much ass I doubt they'll sell. For all HN likes to spin acquisitions as victories, 95% of the time they are the final denouement of a defeated startup. When a startup is doing well, ambition takes over and selling is usually out of the question.
NFC payments? Google Wallet?