I know they got rid of the zombie virus before, but now that wardrobe skins are a thing and you can just remove them, is the potion useful for anything else anymore?

I don't think it does anything anymore, once you unlock a skin in your wardrobe there isn't any need to cure it. But I haven't tried to use one since the change, so I'm not really sure.

I would guess the only real use for it now is collecting it in a pet's TC or a gallery.

I thought so. It doesn't necessarily fit into any of my pet's TCs so I'll see about selling or giving it away rather than testing it and wasting it. Thank you though <3