With Heroes of the Storm and Heart of the Swarm, I feel like Blizzard need to continue this trend with Hellbeasts of the Scourge, a Diablo 3 expansion that features a dungeon themed entirely around hell. Like, proper hell, not their namby pamby hell.
WoW could go with something like Horde on the Surge, an expansion where the Horde find new power and attempt to take Azeroth by force. It's a PVP-centred expansion mostly that will change the areas that belong to each faction on PvP shards. The Alliance have their own story that involves them developing their power in response.
Anyone else got any HOTS new ideas for Blizzard game expansions?