A simple retype, new ability, or new move can really make a big difference. Togekiss and Azumarill are seeing much more usage and have a shot at OU just because of a simple retype. Scoliopede has gone from complete zero to hero with his fancy new Speed Boost, an ability which by itself makes an entire playstyle like baton pass even possible. Exploud is just now seeing the light of day with it's new Boomburst move. About a hundred competitive pokemon are about to get an update, including OU veterans like Jirachi and Infernape, any one of which might get something game changing. That's not even counting new Mega Pokemon (Latios and Latias are confirmed to get Mega Evos) that might be lurking in the game code waiting to be unleashed when pokebank is released. I agree that Mega Gengar will most likely still be broken then but the problem is we just don't know. For all we know we could get a better shadow trapper that completely outclasses Gengar or some ridiculous pursuit user that makes Gengar about as useful as Dugtrio. We don't know and so we may as well wait a couple weeks to find out.Pokebank will only change a few things we know so far:
- stat changes for mostly irrelevant to OU mons that won't matter until UU/RU/NU are made
- A few potential egg moves, that except for maybe Goodra getting recover, won't really change a thing.
- Non in XY mons getting a few new moves. Only major one I can remember is Tornadus apparently getting Aeroblast and Entei with Sacred Fire(only really relevant for the ones of us that like to play RU sometimes), both of them hinted/confirmed by the maison(or just ai cheating that is also likely).
None of these look like something that would make Gengar easier to stop. or slightly less effective at what it does.
And PGL pretty much confirmed nothing else is getting fairy-type. This should be obvious after a mon with everything moon related(Cresselia) didn't get it, but still listing it for those that don't know that.