The previous version of these spells had them auto-trigger upon depletion of certain runes. Most Death Knights felt this made them have to artificially hold back on abilities or muck up damage rotations simply to save the abilities for when they were needed. Having them usable should, of course, clear that up, though there's some argument now as to whether the nerf they took in the process was too harsh.
In other news, They're looking at firming up other passive tanking abilities as well. Deep Unholy, they say, may need an additional passive tanking talent to match Will of the Necropolis and Acclimation. Anti-Magic Shell will also be getting some buffs. It will be made non-dispellable at the least, and may include immunity to DoTs and magical debuffs. Unholy's tanking ability has somewhat suffered from the removal of Lichborne to the Frost tree, so it'll be nice to see it get some extra utility.
There's some concern over Frigid Dreadplate at the moment, as the 50% slow will not work on most boss mobs. Of course, 50% is a bit steep for a boss mob, so it's understandable, in my mind. It will stack with Thunder Clap on regular mobs though, which does mean at the least that Frost Death Knights have some nice synergy with warriors in 5-mans.
There's also some concerns about Bone Armor and the Unholy tree from some quarters. While Bone Armor, thanks in part to a shorter cooldown, does seem to have superior mitigation against a single target, Unholy also seems to be the AOE damage and tanking tree, with abilities that strengthen Death and Decay and Blood Boil as well as extra abilities such as Unholy Blight and Corpse Explosion. However, since Bone Armor only has 4 charges, they could concievably be used up very quickly in a multi-mob situation. Hopefully, the new longer internal cooldown may help that bit, as could the possible new late Unholy tanking talent.
Most of these changes will be coming with the next build, so we'll be able to test them then and see how they work off paper and out in "real" tanking situations. Right now, it might be nice to see a little bit more base mitigation ability, although having Toughness and Anticipation and Blade Barrier in the first tier of each tree may help a Death Knight tank a bit on that end.