"Super-singular elliptic-curve isogeny cryptosystems" has been
broken classically, isn't it?
There are no "Quantum Computing Threats". QC simply couldn't scale exponentially, and no workarounds would "enable" it.
It all comes down to the noise, the random events altering the energy and space. There's no way to hide from it. Random gravitation pulse, a single neutrino passing, and it's all gone. Somebody making a step far away - all gone. If 256 bit private key is to be found - somebody laughs on the other side of the Earth - all gone. Most of the time such system have to represent at least 2
256 states simultaneously... well, even if it was 2
128 the noise eats it all.
Some people put hope into "quantum error correction". Unfortunately the error correction system, while canceling some noise, produces more of it, since the process takes time and space.
The more time passes - the more noise is accumulated. The bigger space a qubit "occupies", the more noise as well.
It would be wonderful if I'm wrong, but for now the above looks correct.