Long-term data protection, storage of old encrypted traffic and quantum cryptocalipse
I can't agree with bullet 3. of the question stating quantum computers are getting stronger with a good pace (82-qbit computer last year, 512-qbit computer this year), at least in a context of cryptanalysis.

Even the marketing people praising the device alluded to do not pretend that it is of a kind useful for cryptanalysis: they state about it:


  The types of problems the quantum computer is designed to solve are called discrete combinatorial optimization problems. The most cited example of this kind of problem is the “traveling salesman problem”.


Importantly, there is no claim of exactly solving almost all TSP of a given size, which would be a big breakthrough with potential applications to cryptanalysis. This marketing text proceeds to describe how better solving the traveling salesman problem as applied to US trucking could be of economic and ecological significance, without giving any evidence that today's TSP solvers can't handle that task satisfactorily.

In a recent scientific pre-publication linked here, the term " quantum annealing processor " is used to describe the device. Entanglement of only 8 qubit is claimed (a single out of 8x8 arrays of 8 qubit). Even if these 8 qubit where a quantum computer, and if all 64 arrays where functional, 64 arrays of 8 qubit would not make a 512-qubit quantum computer.



Enough expressing my strong doubts about the usefulness of Quantum Computers for cryptanalysis in a foreseeable future, let's get positive.

To protect against hypothetical Quantum Computers of a kind and size useful for cryptanalysis, using twice larger keys for symmetric algorithms is ample; AES-128 is safe today against key search, I bet AES-256 will remain resistant (in practice, to all but side-channel attacks) even with quantum computers, for decades (the most forward-looking may want to use Rinjdael in its 256-bit mode with perhaps an even wider key).

Now there's the problem of asymmetric algorithms (used when we want a private key not shared with anyone else). The mainstream asymmetric algorithms (RSA, ECDSA, DH, ECDH..) with today's key size are conceivably not secure against said hypothetical QC. Update: and, contrary to what I initially wrote, forward secrecy can't fix that. Protocols with forward secrecy, like some options of TLS or IPSec, can prevent past intercepts to be broken in the event of future leakage of private keys, including by use of future QC. But we do not know practical means (wich excludes Quantum Key Distribution) to fully protect us against intercepts made today, and analyzed in the future using an hypothetical Quantum Computer of a kind and size useful for cryptanalysis, and able to break the step of a key exchange protocol that built an ephemeral/session symmetric key, using typically some variant of DH or ECDH. Towards that, we need better/stronger asymmetric algorithms; I'm incompetent about it. In the meantime, we can use large asymmetric keys (particularly for the scheme building an ephemeral/session symmetric key); that's arguably at least of some use against QC.

And we should care, a lot, about much more mundane things than QC; like compromise of our computing platform, side-channel attacks, bad TRNGs, implementation goofs, and traffic analysis.