To me it's a sign that the developers have nothing but the big, final presents left, thus having to use the craziest ideas to quickly craft a new expansion in the meantime.

Whether the upcoming big battle is left for the end of WoW or the start of WC4 is a matter of opinion... But we're all skeptics here. Of course it's for WoW.

One way or another, finishing up the big "neutral" threats (the Old Gods and the Burning Legion... and a possible rage against the heavens VS the Pantheon) leaves little challenges ahead of the players. You can't surprise someone with Interdimensional Illidan's Ill-hearted Demonic Host after they've just defeated Kil'jaeden.

Thus, we resort to padding. "Filler episodes", if you will. Something presentable, but ultimately off-topic.

How many "padding expansions" do you guys expect to come before the closure?

I'd say we've got 2 more solid expansions left. Azshara/Naga/High Seas/Terrors from the Deep, and the Burning Legion finale.

Anything else that comes before that, like MoP and WoD, is just filler. How many? No idea, that's upto Blizzard but it's clear they're milking the WoW cow as hard as they can by this point.

It's filler, pure and simple. I don't mind filler per say, it's just after Metzen was very explicit "MOP IS JUST A BUMP IN THE ROAD! WE'LL GET BACK TO THE MAIN STORY SOON!". I was fine with MoP because it rounded off the Alliance-Horde War plot which was the biggest tumour in the narrative. It did a poor job of it, but at least it was over finally.

I expect we'll get Emerald Dream as some more filler, potentially between Azshara/Legion. Heck, it wouldn't shock me if they split South Seas and Azshara into two separate expansion packs. I know they claimed that they couldn't do ED because 'too much green' but it wouldn't be the first time they've gone back on their word about this sort of shit. See "MoP is just a bit of filler!"

I think Azshara expansion and Nyalotha expansion could potentially be different parts.

Potential for a filler exp also exists in form of True Azjol Nerub.

That most of the good writers are working on bigger and better things. Leaving Kosak to write another expansion.