Been diving into theoretical quantum computing and encryption.

As I understand it, Powerful quantum computers will:

Likely be capable of finding a public key from a 160bit hash of a pub key, and compromise privacy if an interested party had the means.

Very likely still be a long way from cracking 256bit AES, so private keys will be safe.

Will only practically serve to increase hashrate and security against double spending.

When we get there though, I'd expect the network will work to incorporate quantum encryption for privacy and security in some fundamental way. More against the next leap in computing than as an imperative against quantum computer attacks. Though I can't imagine how.