There are comments later in the thread that state that it was implemented though.
Yeah, I do all my tags by hand

I like zoning out listening to music and tinkering with metadata!
I use the Publisher tag as a stand-in for "Record Labels" and there are plenty of records that have more than one label, even on the same specific release. Obviously not the end of the world if I have to use a custom tag for it but it would be nice if I could just use Publisher.
I'm not looking for a [...] button, just the functionality that comes with being able to split a tag.