Self-portrait is basically from the same era as fictional persona was, and thus was tainted by the same mentality that led fictional persona to become utterly redundant - while fictional persona tried to do something no one thought was needed (a sub-tag for artist self-insert, for artist personas), self-portrait tried to include something it should not have in the first place (personas).
I argue that the tag should be extensively gardened and rendered so that it is just explicitly for artists drawing their real life selves, because I'm certain that we have a good number of posts which depict just that (effectively becoming the reverse of what fictional persona tried to be before it got coopted by MMORPG players). It would certainly be far more useful than fictional persona would have been, because you'd think there'd be far more artists drawing personas rather than their real selves for privacy reasons. It would also justify the tag keeping its metatag status, because knowing it is their real selves would likely count as meta knowledge.