Release on Xbox and Playstation, bonus points if it releases on Nintendo's consoles
Instant back to #1
popular MMO. And at least for FXIV, its on consoles and plays fine on consoles even though there is a ton of abilities to use.
Or ESO has the same amount of abilities (to use at one time) as WoW BFA does, and it plays fine and is so successful (well partly, its a good MMO too) because its also on consoles. That increases the amount of attention it gets and increases player count.
Of course "easy" probably not entirely accurate, but it be the easiest way to greatly increase sub count.
Would probably need to do the ESO approach though and do a hybrid sub model, but works for ESO on consoles so no reason it wouldn't work for WoW.
But if blizzard really cared about staying as the #1
MMO, that be the way to do it. Besides, most MMO/pc gamers have already played/tried WoW at one point in time, and there are a ton more console gamers than PC gamers in general. It be a quick way to success. Plus console gamers tend to buy cash shop stuff even more than PC gamers do, so that also increases blizzard's income on top of that.