The most interesting issue in the opinion concerns ratification of the FISC's interpretation of Section 215 by Congressional reauthorization of the Patriot Act. I think the decision boils down to a judgment that there can be no ratification by legislative reenactment absent public knowledge of the intervening judicial interpretation. As a policy matter, I think the best defense of that would be the argument that ratification by reenactment is a disfavored doctrine because it changes the meaning of a statute without changing the words (perhaps even without express, specific legislative acknowledgement of the change), and therefore should be confined only to the most obvious cases, such that a categorical exclusion absent public knowledge is appropriate. I am not sure that is the correct argument as a matter of policy, and even if it is, I am not sure it is the correct argument as a matter of law (rather than policy). But I think I understand the view, at least.
The really interesting question, beginning a few weeks hence, is whether Congress will do something intelligible here before Section 215 expires. For example, a straight reauthorization, of the sort Senator McConnell has proposed, could now give rise to arguments, under variants of the ratification-by-reenactment doctrine discussed above, by both sides in the debate!
More broadly, it is a puzzling moment, both domestically and internationally, for surveillance law in particular, and for national security law and policy in general. It makes a striking contrast to the two major moments of policy convergence in my lifetime ---the Church/Pike reports, and 9/11---where only a few brave souls like Laurence Silberman and Russ Feingold felt the need and had the courage to voice dissenting views. Today, we have a strongly divergent environment, with the Snowden disclosures and governmental reactions to those disclosures on one hand, and the recent attacks in Paris and in other locations, the rise of ISIL, and the increasingly unstable environment abroad (e.g., Yemen, Central African Republic) on the other hand, combining to create a whipsaw that threatens any effort to chart a middle course.
That divergence exists both within the U.S. and also between the U.S. and the rest of the Western world---or at least the UK, France, and Canada, each of which has, recently, taken legislative or other measures to expand surveillance authorities. Arguably, of course, the European intelligence services have for a long time quietly enjoyed more legal latitude (by some measures) and less rigorous oversight than their U.S. counterparts; but the very public nature of the divergence today, in favor of broader surveillance powers for non-U.S. Western governments, is unfamiliar to me, if not actually unprecedented.
The effects of this domestic and international divergence could become even more puzzling depending on the reactions of the major U.S. providers. The providers have been terrified of the post-Snowden competitive advantage, in the form of perceived relative immunity from surveillance, enjoyed by their European competitors. It has caused them to resist, in part and wherever possible in public, some of the U.S. government's discrete requests for data, and also broadly to support a treaty-based, international surveillance regime to level the playing field and thereby remove the competitive advantage. In the last couple of weeks, however, with the legislative actions abroad, today's CA2 decision and perhaps the upcoming Congressional (in)action in June, the environment supporting the providers' strategy may be upended. If present trends continue and certain matters break in certain ways, it's no longer entirely fanciful to imagine U.S. providers trumpeting the competitive advantage to consumer privacy of the U.S. system of intelligence under law (and its general requirement for advance review by neutral and detached magistrates), and publicly resisting at least some data requests from the UK and other foreign governments!
In short, I can't predict what will happen next, but I am certain that it will be very interesting to watch.