While I love the new Deadmines, Vanessa's nightmare phase will be an actual nightmare in M+.
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I think Throne and Vortex Pinnacle could also work; they look great and they have great variety in bosses and mobs. Vortex in particular with those tol'vir packs that move through the defensive fields would be very interesting to see. Plus Elementals was the big theme of Cataclysm far more so than Dragons and with those three we get 3 out of 4 Elemental planes.
And given one of the early enemies in Dragonflight is Elemental Dragons, using Elemental plane dungeons would also fit thematically. Vortex and Stonecore both have elemental drake bosses that drop mounts.