Side question: if quantum computers fulfill their promise, won't they break encryption as we know it? Are we ready for that kind of upheaval?
Quite sure cryptographers are ahead of the curve, they are a conservative bunch. There's multiple finalists in the NIST post-quantum comp with different quantum-hard mathematical properties. An over-abundance of lattice cryptography being standardised could possibly be a problem in the long term though.
Asymmetric public key crypto and signatures being broken is the only real threat, there's no theoretical issues with symmetric crypto, hashing or MAC's.
A quantum break already has a multi-billion dollar bounty on it in the form of cryptocurrency wallets which would be hard to fight against in the form of wages or violent coercion. This is probably the best evidence on Earth that no one actually has this capability.
Note I'm not saying that I actually think someone has achieved this, I just don't think "no one is stealing btc" is a good non-existence test.
If a particular address has never sent coins then an attacker has to perform a pre-image attack against SHA-256 and RIPEMD-160 which even for quantum computers would be 2^128 operations (generally believed to be intractable) and wouldn't even require breaking ECDSA.
Since most original coins have never been sent anywhere there isn't a way to directly attack their ECDSA keypairs.
There are, however, plenty of addresses holding (a lot of) coins whose public keys are in the blockchain, making them targets for quantum computing attacks. An attacker could solve the discrete logarithm problem for a key and forge a signature in a transaction sending all the coins owned by the matching signature to a new address owned by the attacker and the transaction would be accepted by everyone.
There's a standardization process going on for post quantum cryptography at the US NIST. Results expected before the almighty RSA-breaking quantum computer arrives.
There's still a concern about store-and-encrypt-later (i.e. someone can store encrypted communication today and decrypt it once a QC is available), and how relevant that is depends on some unknowns (how many years to you expect your comms to be secret? how many years till a usable QC is available?).
Note that the best known quantum attacks on ChaCha20 cut the key size in half, so 256-bit ChaCha20 should still be fine, as long as your key agreement protocol is quantum-resistant.