All of the fairy pokemon seen and likely to be retyped don't exactly have monster stats or anything of the sort, not like the dragons do, so anyone suggesting fairy is going to be over powered is completely mistaken.I think they will do their job well of curbing dragons, but all you have to do is switch into something with a strong poison or steel move and they will likely bite it pretty easily. There aren't a lot of pokemon in the Meta game equipped with moves like that, but something tells me they are about to get more popular...
Yeah, I don't think there's a lot to worry about a Wigglytuff, even with Fairy-type's changes.