he pretty explicitly states that AES 128 is not in any imminent danger and mandating a switch to 256 would distract from the actual thing he thinks needs to happen.

So why argue about whether AES-256 is worth it if we can just literally replace those 3 characters and be done with the upgrade? This was the smart move already in 2001 when Shor's algorithm was known and computers fast enough that we don't notice the difference. At least to me, it seems like less bikeshedding will be done if we abandon AES-128 and don't have to deal with all the people left wondering if that's truly ok

Then again, something something md5. 'Just replace those bytes with sha256()' is apparently also hard. But it's a lot easier than digging into different scenarios under which md5 might still be fine and accepting that use-case, even if only for new deployments

How would he know? Did he publish papers on it?

You can’t just throw “Grover’s algorithm is difficult to parallelize” etc. It’s not same as implementation, especially when it gets to quantum computers. It’s very specialized.