If WoW became super hardcore, not early Cataclysm hardcore, but REALLY hardcore. I mean attunements for raids and dungeons. A typical mob being able to actually kill a player 1v1. Epic gear only being available in raids/top-tier pvp, blues only available in dungeons/mid-tier pvp, and greens being the standard for a normal player. Legendaries being reserved for something like the top 0.5%. Quests being challenging with Blizzard actively encouraging grouping more often. Classes with rotations that call for more skill but with a higher reward when very skilled. In essence shit DPS if you suck, but infinitely amazing DPS depending on your skill.
Gold being more difficult to come by and professions taking much longer to level but with more powerful rewards. With the earlier dungeons in the attunement system being easier but the later ones becoming increasingly difficult, culminating in the end boss of the expansion that not everyone gets to see. A much more compelling and rewarding PvP experience, with a focus on making WoW a legitimate e-sport.
And in general, just creating a community that does not reward bads or encourage being a scrub. A community where every players performance in a dungeon counts, and where accountability is much higher. A community where people strive towards a goal and work hard to reach it. A community built on competition and dedication. With all of this starting with Blizzard themselves encouraging the community of yester-year. A return to the essence of WoW.
-Would you like a much more hardcore WoW like this?
-Would this be a smart business move for Blizzard to make, or would it backfire?
-Would the positive word-of-mouth/reviews resulting from this be enough to spark an influx of returning players?
-Is it possible that the subscriber influx would come after some time when the community readjusts, and not necessarily immediately?