Unless Blizzard has some real story shake-ups and a phenomenally tuned raid on the horizon, I'm honestly expecting the sharpest player decrease to set in within the next few months. The expansion itself has some interesting ideas, but sticking to a World Quest grindfest is quickly becoming the norm, and the Island Expeditions aren't exactly exciting.
Capcom perfected the combat formula over countless releases, but it wasn't until Monster Hunter: World that they stripped away what ultimately was never much fun to begin with. You spend less time spent preparing, and more time actually fighting. And sales figures suggest, as we all expected, that Capcom really had something special sitting under all that bloat.