So we find the whole "Not Provided" issue really perplexing. It's nothing to do with SSL and encryption, Google simply choose not to pass on referring keywords unless you're paying for Google Ads. It seems to be nothing to do with privacy - which is of course Google's apparent reason for implementing this.
But this is a dreadful fudge, and Google are smart. Full of clever folks. We can only think that either the financial imperative got hold and drove the decision, and/or that perhaps some odd set of circumstances came together such that an idea that's not apparently well thought through and not well presented just got the go ahead.
We can imagine a number of Googlers sitting around afterwards wondering "wtf, how did that happen?"
Perhaps it all began with a conversation along the following lines:
Some Cubicle in A Googleplex:
Googler 1: "Hey, how's it going?"
Googler 2: "Yep, great, you?"
Googler 1: "Yep, awesome. Got something need to run past you".
Googler 2: "OK, go for it."
Googler 1: "We need to sell more ads".
Googler 2: "Well, yeah, duh".
Googler 1: "How about this: we stop passing on referring keywords to analytics for natural search, but let keywords through for paid ads".
Googler 2: "Uhu. It's not going to generate much extra sales is it? I mean, are people really going to buy extra paid ads just to see keywords?"
Googler 1: "Hey, some will. And that's extra sales. Which is an extra bonus. We could say it's both our idea.".
Googler 2: "Ok .... well, let's think this through for a moment. We can't just say that Google is screwing natural search just to pay more ads can we? I mean, Don't Be Evil and all that."
Googler 1: "Nope. But here's a thought: we can say it's a privacy issue. We can say that if people choose to make requests of Google via SSL, we'll respect that decision, and not pass the referring keywords onto analytics. If they don't use SSL, we will pass on referring keywords".
Googler 2: "Yeah, but not many people make SSL requests to Google at the moment.".
Googler 1: "Aha. We can force them though can't we. And we've got a deal with Firefox. And ... we've got Chrome. Kerching baby. New spot in Tahoe here we come. Need a bigger space for all my boards anyway."
Googler 2: "Yeahhhh, doesn't really work though does it? Respect privacy, except if you're paying for Google Ad's? That's a bit of hole in your plan dude."
Googler 1: "Nah, you're making too much of it. We're Google. If we say we're respecting privacy a whole bunch of folks will just go along with it. I mean, only webmasters and seo nerds will get twisted any.".
Googler 2: "Hmmm, dunno. What about the Google Analytics Premium customers? Surely, they'll be a bit pissed?"
Googler 1: "I know! Google Analytics Premium customers can have access to ALL referring keywords, whilst 'standard' Google Analytics customers can have limited access. So, although keywords will gradually be hidden, at least GA Premium customers will be able to see all keywords that there are. There'll always be some wierdos who opt out of SSL, so there'll always be some keywords - and if you have GA Premium, you get the few that there are!".
Googler 2: "Errr, OK, guess so. Extra dough I suppose. Worth a shot I guess.".
Googler 1: "Ach, Tahoe, or Hawaii - can't decide. What do you think?"