Durendil did it two days ago. He, a hunter, got the Gold Tanking achievement in the proving grounds. What's awesome about this is the proving grounds make it so you can not overgear the content. Previously all the pet-tanking and "extreme soloing" we've done, we've done it while having killer gear -- at the minimum a tier above the content being solo'd.
I took a stab at it and realized I needed a fully new bar with full new macros keyed-off of specific pet tanking talents and glyphs. Threat from chain-MDs isn't quite enough. Not having a taunt, you have to pick up the adds immediately. There's only one thing that he did that I was thinking of doing different. I was going to use the Distracting Shot glyph. But I guess that might take away from other more important glyphs.
I've been checking the lists for a week or so. Warlocks can do it. They have a decent tank and can fear bomb +DoT. Durendil is the first hunter.
Congrats! Here's a link to the video.