I still think we'll see Mega Gengar banned. Gothitelle and Wobbuffet are so different from it that they certainly aren't good comparisons. Gothitelle is slowwww and weak. (Specs Gothitelle is actually weaker than a Modest Mega Gengar...) Wobbuffet has no way of attacking. On the other hand, Mega Gengar has 130 base Speed with a very, very good movepool that can be customized to trap basically anything you want. The fact that it can come in on anything that's been weakened and take it out without the opponent being able to do anything about it is a pretty strong case for Uber status. The only downside to it is that it needs a turn to activate Shadow Tag, which isn't that big of a deal since Gengar is a good Pokemon in general. And look at Shadow Tag Chandelure, wasn't it really overcentralizing in DW OU? I don't see how Mega Gengar will be any different. Buuut I haven't played gen 6 a lot yet and we're still early on, so we'll see what happens.
Also, Mega Blaziken seems pretty likely to get banned just like it was last gen. I don't see many things changing for it since then, but at least sun was nerfed.