Aside from rain teams, I really think that its hard to counter play imo. Besides chansey i see no real safe way to approach this mon outside of, as I mentioned earlier, rain teams.
Volcarona fortunately didn't gain access to Earth Power like it was rumored to, and it didn't even really gain any notable tools besides Heavy-Duty Boots, but it is incredibly likely to do just fine with what it already has. Without Heatran, Volcarona is completely free to run Psychic so there isn't really any 4MSS to hold it back. Luckily, we still have Pokemon such as Chansey, Toxapex, Kommo-o, and Rotom-H available to check it, but will that be enough, or will Volcarona prove to be too much for SS OU? What do you think?