Scaleface posted all his information (i.e. the name and class and some other facts) before the 4chan post was made.
Meanwhile, the 4chan post got the name of the class wrong (Invoker instead of Evoker), said there would be covenants for the Dragonflights (there aren't), said that the main characters would be Alexstrasza and Wrathion, when Wrathion really was only mentioned to be active in one zone, fails to mention Kalec or Khadgar (who is probably gonna be our actual main guide), and mentions Murozond as the villain when Scaleface said there is no real appearance towards the villain yet, but it seems to be Galakrond.
Scaleface is 100% legit and there is no doubt about it.
The only thing the 4chan leak got right were things Scaleface revealed himself hours prior to the post. Scaleface mentioned a talent revamp, Scaleface mentioned the names, the amount of zones was obvious given the last few expansions.
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Season 4 certainly won't be long though. All the loot changes hint at that, the affixes seem more in the players favour than being difficult, the most desirable reward is obtainable from LFR.
Season 4 will probably only be 4 months.