Have you seen any attacks on WSS servers on localhost with both explicit opt-in (via the Origin header) and implicit opt-in (via public DNS record and TLS certificate for that public DNS record) and additional mutual authentication (as in the case of Dropbox)? I doubt there are even a handful of people who have setup something like that (I used to think that WSS on localhost was not even possible because of the self-signed certificates not validating).

And that is a specific scenario for which you can easily create a permanent exception for, without requiring the user to start Chrome with a command-line flag.

You can block WS on localhost by all means.

But blocking WSS on localhost after someone has gone through all the trouble of setting up a public DNS record, and CA-signed SSL certificate which validates against that FQDN (this is not just about public DNS localhost record services) makes no sense to me, and seems to be outside the intent of the original bug ticket.