My vote is don't ban Shadow Tag
Try to have a Gothitelle in your pvp team, you will see it's not that useful at all. I have tried one in my team and it's definitely the last useful pokemon and sometimes a waste of slot. Gothitelle only good again some special-attack staller like Blissey, Venusaur, Clefable. And every offensive or Dark type or U-turner, Volt Switcher, Roarer pokemon can counter it easily, like literally. In my opinion, Gothitelle is easy to counter than the combo of Blissey and Slowbro, or even Talonflame force everyone to carry a rock type. So why ban a pokemon if you can counter it in many ways? The meta game now is full of similar stallers and it looks so boring to me, and all you can think of is ban this and ban that? God just free them, I want to see a meta game that's full of surprise and creativity, not like this.
The reason Smogon banned Shadow Tag is because Gothitelle can hold choice item then use Trick to swap to opponent, this way it can break everything, this call Literally Satan Gothitelle. But in PRO, Trick is not working. Finally if you ban Shadow Tag, then Arena Trap has to be banned as well !