• does that still exist in bfa?
• does it actually work in a way that makes sense for this?

Fixed with "compromise" - all player controlled NPCs will be treated as off-tanks. That seems to be the simplest way, since the API is terrible for this.

Would love to see this implemented. Black Ox still perfectly functions as an offtank.

I find this to be pretty useful for monks especially in mythic+. Currently, there is no way to tell whether ox statue or a party member has aggro. Please implement this feature!

+1
would also be amazing if Balance Druid Treants, Shaman's Earth Elemental, Monk's Niuzao, ... and optionally hunter and warlock pets could be treated as offtanks as well. I tend to panic when losing agro as a tank in m+ only to see that it was just a treant.