Not going to happen. Ever.
AT&T is trying to get rid of unlimited users, not make it easier for them to go through data. AT&T offered me 6 months free of 5GB plan with tethering to give up my unlimited, I told them not a chance.
Nope. tethering on unlimited plans has never been allowed. And if you're on an unlimited plan after all this time, it's likely you are very low on their priorities in terms of loyalty and retention.