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.
To reiterate the issues with your proposal: Public DNS pointing to private/localhost is in fact a component of many of the attacks we're concerned about. HTTPS on localhost doesn't do anything because the transport is already secure (which should be simplified in a future change in Chrome's content handling). And given that the major concern is weak/permissive servers, we can't rely on the WS(S) server implicitly protecting itself by enforcing the origin header.
With the server being already running and meant to be connected to from a browser (as combination of WSS and proper localhost cert is proving), listening and explicitly allowing the client to connect, what threat is supposed to be there?