...It sounds as if this is intended to only affect existing tags, not the creation of new artist/character/etc tags, correct?

If that's the case, then I think something may have gone slightly awry with the coding- I was just now trying to create a tag for a previously-untagged character and it failed, giving me the following error message:

Something went horribly wrong...

Unexpected error (150ce45d4a5ada940fb989bcc6b0cabc)

Give this to an admin to report the issue: 150ce45d4a5ada940fb989bcc6b0cabc

I double-checked the Tags page for an entry afterwards, and even with 'Show empty tags' enabled it's still not finding anything. If I'm misinterpreting the announcement or doing something wrong, please let me know, but if not then it looks like the update broke something.

Update
I was able to create the new tag after all, but I had to do so by creating it as an un-metatagged general tag and then manually changing it from the tags page. So novel tags /are/ still possible- but is this how the implementation is intended to behave?