Right off the bat we have 5 major glyphs competing for three spots. All 5 are threat related.
Rune Strike is straight forward increase in TPS for all DK's. Given the changes to Blade Barrier it's not my favorite, but it's still damn good.
Death and Decay is an oldie but goody. Who doesn't want an additional 20% damage on our highest threat AOE tanking ability.
Dark Command may or may not be the biggest tanking DK glyph in the game. It is situational but when you absolutely need the taunt to hit, this glyph puts a melee hit capped tank at the hit cap for their taunt as well. If Ulduar has lots of mechanics like Gluth where two tanks have to taunt off of each other this will be required.
Glyph of Disease is the much ballyhooed glyph that allows pestilence to refresh your diseases on your current target at the same time as spreading/refreshing them on the AOE packs you are working on.
Dark Death is a straight up threat increase by pumping up death coil damage. Though as a tank this is probably lowest on my priority simply because death coils are lower priority uses of RP than other abilities.
Blood Tank Glyphs
The reality is, Death Strike can apply to all trees but I put it in blood since it is the primary strike FU for blood given the changes to lichborne. More damage equals more threat. This will be a common theme.
Vampiric Blood brings the healing benefits to this talent up to 25% uptime given the 2 minute cooldown nerf.Frost Tank Glyphs
Unbreakable armor buffs the mitigation of this talent even further. Like all our mitigation cooldowns this took a nerf but for the 20 seconds its up this will go a long way to ensuring you survive what ever is thrown at you.
Howling blast, Obliterate, and Frost Strike are all threat enhancers. They all contribute to your damage output which will ensure the mobs hate you that much more.
Unholy Tanking Glyphs
Bone shield's two extra charges becomes even more valuable as our avoidance and BS's cooldown got nerfed.
Unholy Blight's 10 extra seconds frees up more RP for rune strikes and deathcoils to increase your threat.
Scourge Strike remains the same and continues to refresh your disease on your primary target.
It remains to be seen whether Dark Command will be required. Right now if you miss a taunt on Gluth or the 4 horseman you can survive until it comes off cooldown with good gear and decent healers. That may not be true in 3.1.
Assuming Dark Command is not required my immediate reaction is to take Vampiric Blood, Disease, and Rune Strike for blood tanks. I'd lose disease for Dark Command. While refreshing diseases is nice for main target and AOE, I'm not hosed if I don't maintain 100% uptime for either single target or AOE.
My Frost Glyph selection would be Howling Blast, Unbreakable Armor, and Frost Strike. Since I've never tanked as Frost I won't be offended if any Frosties suggest otherwise. If I need Dark Command I'd probably drop UA. 20% on oh shit is nice, but the likelihood that the 20% is actually the difference between a wipe and a kill is probably less than that of a missed taunt.
Unholy tanks will have to take Bone Shield. With impurity I would also grab Death and Decay to take advantage of the AOE synergy. Last I would grab Scourge Strike to keep my single target threat up. The disease glyph doesn't do anything for AOE threat and we will be spamming SS on our main targets anyway. If I have to lose one for dark command I'd drop the DnD glyph.