Word is out from Ghostcrawler himself. http://us.battle.net/wow/en/forum/topic/4253968049#12
I'm bummed
What he said, for those too lazy to click the link:
Just to make our intent clear, the Glyph of Demon Hunting isn't intended to turn Demonology warlocks into a tanking spec. You won't be able to queue as a tank for Dungeon Finder for instance and won't have the survivability or tools of say a Protection paladin.
Historically, warlocks felt tankier than other casters and could even off-tank some encounters. We have made an effort in Mists to recapture some of that flavor. A warlock with this glyph should feel like they are about as effective tanking as an Arms warrior who pulls out a shield and swaps to Defensive Stance, or a Feral druid who goes into Bear form. You might be able to off-tank adds or pick up an actual boss for a short period of time if the tank goes down.
To make warlocks an actual tank would take more significant changes. For example, we want tanks to have to pick up separate tanking gear than their DPS gear (this is even true of druids) and want tanks to have to give up some of their DPS potential in exchange for their survivability. In short, it needs to be a commitment, and that's the sort of thing that needs larger gameplay changes than just a glyph.
That shouldn't stop the glyph of Demon Hunting from being fun though. As you can probably tell, we are trying to make even the major glyphs more about character customization and fun.
End quote.
Allright, I went to bed and when I woke up it seems Ghostcrawler made another eyebrow raising comment, sort of mollifying me, even though I still prefer the idea of being a full time tank.
What he said:
As some of you have pointed out, the glyph of Demon Hunting in your beta build doesn't deliver on what I described above as the design. The newer version of the glyph, hopefully available in the next beta build, allows a warlock to toggle in and out of the off-tank / survival mode, more like the druid going Bear or the warrior going Defensive.
The new shapeshift granted by the glyph is called Threatening Presence (PH) and adds Taunt and Fury Ward to the normal Metamorphosis toolkit. You still get the damage reduction from mastery instead of the damage boost from mastery while in this form. You can also choose to go into normal Metamorphosis even if you have the glyph. Let us know how it feels.
We appreciate all the feedback and passion on this topic. We expected this glyph would serve a pretty niche community and were surprised at how many players were excited about it. We are still in beta and are still very much experimenting with what kind of gamplay we can deliver in glyphs.
End Quote.