The liberal justices voted as a bloc together in CLAPPER, DIRECTOR OF NATIONAL INTELLIGENCE, ET AL. v. AMNESTY INTERNATIONAL USA ET AL. to try to challenge the constitutionality of warrantless wiretaps, and I expect much the same from Kagan, Ginsburg, Breyer, and Sotomayor in this case.
Of the conservative justices, Roberts, especially given his tendency to try to hit some home-run majority rulings for his legacy of being a "by-the-rules" arbitrator, and his pronouncement of privacy issues as being the paramount constitutional issue would be most likely to flip with the liberals. With that said, his previous defense and work on behalf of Bork, and his theory of a lack of privacy in the Constitution does leave a bad taste.
Justice Kennedy unfortunately cannot be counted on when it comes to privacy issues. His majority opinion on Skinner v. Railway Labor Executives enumerating that the government could violate the privacy rights of railway workers by subjecting them to drug tests due to a "special needs" exemption where the Fourth Amendment could be ignored if it was deemed to be in the overriding interest of public safety is the basis of the NSA's metadata collection program---see: http://www.nationaljournal.com/nationalsecurity/how-justice-...
He's still the second most likely to flip because Scalia, Alito, and Thomas are basically lost causes. Scalia basically called a general right to privacy in the Constitution rubbish, and it's unlikely either of the three will bend their ideological bent that the "national security agencies" know best.
The votes might be there. It probably hinges on Roberts. But significant positive changes to how the American government deals with privacy issues could happen. Again, the votes might be there, which is better than never discussing the issue at all (or discussing them in dark, dank courtrooms nobody hears about).
Cause for hope goes exponentially up if one of the conservative justices retires and is replaced by a young liberal justice attuned to technology much as Kagan is. If that happens, this likely scenario becomes a most likely scenario.
Wildcard: The Supreme Court actually doesn't know anything or very much at all about technology. They still pass paper briefs among each other instead of email...a strongly written amicus brief in this situation by technology-savvy leaders could well tip the balance.