Banning a specific set would be like banning SDYache Chomp. Different.
Not like it matters. Nobody with half a brain that actually cares about how well they do will bother to use Gochiruzeru or Wynaut in OU anyway. I guess it'll matter in UU or NU, but whatever. Those don't exist yet.
And I know that's not the point. But if you can't program it to only prevent Shadow Tag on Shandera and/or Wob, then it's not hurting a whole lot to ban it from all of them. I don't know how programming works though, so I can't really speak in that regard.
1. People have already looked in the game data and discovered Gen V Pokemon don't have overworld sprites to use for Dream World. Smogon has already stated a Pokemon MUST exist before suspect testing (aka be usable on Wifi), it ST Shandera EVER happens, it'll be the third game, by then, UU and NU have stabilized. And its not just Gochi and Wynaut in lower tiers. Wob got a nerf too with Encore, and its in a metagame where stuff hits harder. There's a small chance it might not be Uber either, but what if ST is? Then now you're hurting the OU metagame too.
2. They've already programmed ability+Pokemon combination bans. That's why you can't go into Wifi with unreleased DW Pokmon.
And I'm pretty sure NU and UU will evolve perfectly fine, taking away Shadow Tag from about 2 Pokemon that'll fight in it is not really that big a loss. And they have other abilities to fall back on.
As Circa said, they might be top-level UUs or NUs too, and those metagames are just as much of a metagame that OU is. Remember, OU is just the most popular metagame, that doesn't make it the only important one. You shouldn't wreck other metagames when you could simply ban the ability on a single (or if Wob gets called broken, two) Pokemon instead.
What you're doing here is probably hurting other tiers (possibly every single tier from OU to LC) to accomplish the exact same thing as banning something to only change 1/2 Pokemon.
And again, all this would require Wob or ST Shandera actually being called Uber this Gen. Of which I'm sort of against at this point.