pup said:
Given it's technically outside information surely having x_(va) as a meta tag would be a good temporary solution? Then move it to the new category once it's created.
Meta isn't for outside information, it's for information about the post itself rather than what's in the post. The aspect ratio, whether it's a sketch, line art, colored, etc, whether it has sound, if it's animated, the language used, if it's a comic, etc, are all visible aspects of the image (about the only sometimes-non-visible meta tag I can think of is the year, but even then it's more often tagged when the image has the year printed on it). And a properly tagged image can have a fair number of meta tags already, so dropping VAs there even temporarily would create a mess. Lore tags is a better place for outside information, and is less used in general, but only admins can create them, and I don't know if VA tags will be subject to admin approval (I doubt it, but I can't say for certain).
In either case, even if VAs are temporarily tagged under a different category, I think it should at least wait until there's an ETA for the new category. Otherwise if the category takes too long to be made or the idea just silently falls apart (e.g. the people working on it leave or can't work on it anymore, and no one else picks it up to finish it), we wouldn't want to leave a bunch of tags in a category they shouldn't be in.