I think stall is alive and well with the number of viable mons that fit into stall teams. Things like Suicune, Toxapex and Pyukumuku have ensured that with the right team support they can stall out some of the biggest offensive threats in the game. And cores built around some combination of Clefable, Chansey, Skarmory, Sableye and/or Ferrothorn, plus Dugtrio, provide OU with a particularly vile form of stall. I agree that HO and BO are likely the most viable playstyles right now. But as more offensive treats look likely to be suspected and banned, it's only a matter of time before stall gets its chance.