That article is a little misleading. Sites that pull data of active subs place total in the millions, a bit over 2 million, and that only counts those in an FC. So the article saying 800,000 to 1.2 million active estimate is waaay off. An article I saw published like a month ago said active subs were 2.5 million, which is about right considering the estimates from pulled data.
As for king of MMOs, sub numbers don't make an MMO the best in this particular situation. It is a widely held consensus that FFXIV is the best pay to play MMO on the market right now and is now the torch holder. Most of those subs WoW still has is those playing for nostalgia. Most have played many many years and just can't let go, while many have been able to let go. WoW can release an expansion giving players a virtual turd and they'll still see a big burst in subs. Not saying WoW is a bad game. It's a superb MMO, but not quite as good as FFXIV, especially with the past so and so expansions. WoW is only better to those that need parsars/addons and love PVP more than PVE. If FFXIV was released at close to the same time WoW was, FFXIV would have more subs, even if WoW had same graphics quality like being released today. Everquest>WoW>FFXIV>who will be next? Those 3 MMOs are considered the pinnacles of the MMO. And someday, another will be. Maybe EQ Next will be next. Pun not intended.