"Any tort of privacy . . . has to be adaptable to technological change. Coherency and consistency are also vital . . ."
I think the two goals above are mutually exclusive, or at least contradictory.
The only way to have lasting, 'coherent' and 'consistent' protection of privacy is to set out the rights in such a way that they are not so much 'adaptable to technological change' but independent of any technology.
Whether it's a letter or a telegraph or a phone call or an e-mail or an instant message, personal communication between individuals should be protected. And, likewise, whether it's a newspaper or a book or an e-book or a website article, the content that we read should similarly be protected.
The standard should be that any surveillance conducted without a warrant should be limited to what can be gathered by an individual person unaided. Thus, if I am having a conversation in a public place, I don't expect privacy. If I am in my home on the phone, I do. If I am reading a newspaper on the train, I accept that someone can look over my should to see what I am reading. Not so when am reading a book in bed.
Anything further should require a warrant.
Sure, our spy agencies and police forces will wring their hands and cry that they need to be able to see this information and any red tape they have to go through to access it makes it easier for the terrorists and pedophiles to hide. But that excuse doesn't fly because it is not just a matter of requesting access to new types of data that are only being used due to new technology.
If it was then perhaps they would have a point. But it isn't - it's the same types of communications and information that have always existed, just in a different medium. An e-mail is still a personal communication just like a phone call is so if you need a warrant to monitor the latter, you should need one for the former.
It might be a difficult task but we need to develop hard limits and protections that transcend any given past, current or future technologies. The only way to do that is to look at what you are trying to protect. At the simplest, what needs to be protected is the free and private communications of individuals as well as the details of their private lives and activities.
Such laws must have primacy in that any proposed surveillance measure that violates them is invalid.