There is already 4 difficulties
LFR, normal, heroic, mythic.
And yeah, today it's just "new difficulty", which isn't the same as "new content". It also restrict "content" as "raid tier", which is VERY different from Vanilla where content could take many forms, and even the temporary ones (like leveling) where considered long-lasting and valuable, instead of just padding before the "real" content (read : raids).