Turning official artist extras into a tag

BUR #38649 has been rejected.

mass update pool:19122 -> meta:official_artist_extra

I think it's about time to turn this pool into a tag.
Previous discussion: topic #22469

This bulk update request is pending automatic rejection in 5 days.

This bulk update request has been rejected because it was not approved within 45 days.

The bulk update request #38649 (forum #341607) has been rejected by @DanbooruBot.

Is there any reasoning?

Bumping since it was met with overwhelming support but didn't pass