But that probably won't ever happen, because it'd mean declaring the goddamned canonicals and publishing them. Because it's okay to have canonicals as long as we never tell the users what they ARE.

Maybe you're talking about something else, but anybody using the site -- signed-in or not -- can check any tag to see if it's canonical, or if it's associated with a canonical. (Although the word used on the tag pages is "common".)

Examples: Erik Lehnsherr/Charles Xavier is a canonical tag. Erik/Charles is not, and you can see that it's associated with Erik Lehnsherr/Charles Xavier.