Mecha'thun definitely seems more viable than meme. I've already lost convincingly to a Druid that played nothing but card draw, armor gain, Flobbidinous Floop, and Naturalize.
My prediction though, is that this specific combo deck (and Malygos and Togwoggle combos, which also received support...thanks, Blizzard) will stake their corner in the meta and absolutely annihilate slow decks with consistency BUT they will also lose decidedly to midrange (probably mech) decks. It's kind of like the Caverns Below - given enough time, you're probably going to win. But you're also going to sport awful winrates against more aggressive opponents.