I've gone ahead and flipped a long-requested config change for DismissableSiteNotice (which controls local, not Central, site notices) to allow anons to dismiss them.
https://gerrit.wikimedia.org/r/#/c/193090/ https://phabricator.wikimedia.org/T59732
IIRC the only reason the dismiss wasn't allowed for anons was that back in 2007 or so it would have been prohibitively expensive to deal with more cookies, especially since I think local sitenotice was still being used for fundraising banners and such.
My understanding of our current cookie-handling config in the caching layer is that this shouldn't explode. But if it does, or it doesn't seem to be working right, deployers please feel free to revert it and we'll poke at it some more until it works better -- it's an easy config switch, just revert and sync the settings file.
If there's a better process I should follow on this sort of thing do let me know, I don't mean to step on any toes!
-- brion