This kind of observation would already require physical access to the communications medium (e.g. a fiber optic cable). So if you could DoS a quantum encrypted channel by measuring it, you could equally well DoS a classical channel by just cutting the fiber.

If you have secrets to keep, and your adversaries have that kind of access, better a DDOS than a leak.

Edit: This kind of observation would already require physical access to the communications medium (e.g. a fiber optic cable). So if you could DoS a quantum encrypted channel by measuring it, you could equally well DoS a classical channel by just cutting the fiber.

The comment just above mine, which does a better job than me of explaining the degree of access required.

Besides which, it’s not as though you can only use this. You try your quantum channel first, and if it’s down you know you’re under attack, and act accordingly with your Classical backups.

Well, the whole point of encryption is that you can send your message through despite the fact that your adversary can see it.

Replacing that with a system where your adversary can't see your message, and neither can your correspondent, is a downgrade, not an upgrade.

That depends entirely on your application.

Could you give some examples of applications of encryption where the purpose is not to send a message that adversaries may see but cannot understand?

Encrypting data at rest, for example. (Depends on how wide your definition of 'send' is.)