Really? Potential? I was disgusted by the expansion and its themes the moment they revealed it. It was obvious that it would fall flat and fail. It was a poor rehash of TBC in every aspect with horrible writing, bad storytelling, awful zone / game design, removal of flying, no new class or race, bad raids and a massive gear grind (okay we have the gear grind in Legion as well but the overall appeal of Legion is much better).
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There are two routes the next expansion can go, as mentioned quite often in this thread:
a) Filler expansion like MoP / WoD having many sub plots, no real "big bad guy" and nothing very prominent in the Warcraft lore (Faction conflict, Lich King 2.0)
b) Real expansion like Cataclysm / Legion with one major villain continuing the Warcraft lore (Azshara, N'zoth, Void Lords)
They can take route a) but if they do so we'll end up with WoD disaster 2.0. There's no doubt about that.