What Zetsubousensei said is exactly why it was deprecated. We don't really need a tag for it when the site is overwhelmingly female focus to begin with, making it more logical to tag the exceptions in male focus and other focus instead.
Now a tag for when multiple genders take up equal presence is a tag I've expressed interest in in the past (topic #32596), as that is actually pretty hard to search for. Unfortunately, I'm afraid (and Evazion as well) that tag would end up tainted by people assuming it be used for any instance of 1girl 1boy, which is why that tag has never happened.
I guess bringing female focus back could facilitate such a search through a -female_focus -male_focus clause, but you're out of your mind if you think I'm going to honestly propose that. I'd rather tag the exception here, and I have no idea how to do it without running smack into the concerns brought up in topic #32596.