For Warriors, Wryxian offers some insight into the new tanking philosophy. He says that the new high end gear will be designed to add a significant amount of AP to Protection Warriors in order to boost DPS and threat. Between that, and new and revamped abilities and talents, tanking should be a different experience in Northrend for all classes.
Slorkuz's commentary on Death Knights centers around the Blood tree, primarily. The Blood tree, he says, will be a good leveling build because of the amount of healing, but the ideal is that it be as desirable as the other trees in its own way. Frost will be good for crowd control and burst damage, and Unholy for debuffs, but the Blood tree should also be desirable to groups and raids, perhaps through healing.
To this end, they are considering revamping Blood Presence to provide group healing and regeneration. They are also considering adding a dependable party strength buff proccing ability, although they don't want to push it so far that Blood Knights are forced into the melee group like Enhancement Shamans have been in the past.
He also provides some further insight into Death Knight roles in general. Through the use of Frost Presence, every Death Knight should be able to tank, and while each tree has its own individual tanking talents, none of them should feel mandatory. In addition, Death Knight tanks should not feel gimmicky. A tanking Death Knight shouldn't have to sulk at the back of the raid until their gimmick fight shows up.
In addition, he reiterates that every tank should feel like they can DPS. It's a bit harder to completely revamp the existing Protection trees to be DPS-capable because of expectations, he says, but Death Knights can expect to be built from the ground up to be flexible. Either way, every tank class should expect the gap between them and the DPS to be much smaller, both while they're in tank gear and even more so if they switch into their DPS gear.
I have to admit that as much of a Death Knight fanatic as I am, I've been getting discouraged lately as I try and fail to create a "tanking build" for a Death Knight. You just can't grab every good tanking talent as a Death Knight without grabbing a lot of seemingly superfluous DPS talents, and you'll never have enough points to get them all. Even now, I can't completely shake the feeling that they'll eventually need to revamp at least one tree to be the tank tree if Death Knights are going to see any real use as anything other than last resort tanks at most levels.
But at the same time, they do seem to be genuinely dedicated to making every Death Knight tree a true hybrid tree. Blizzard seems to have a plan that's coming across very well in these posts, a plan to make tanks less talent dependent and more flexible. If they can pull this off, I think it'll be a very solid strike against the tank shortage that seems to be afflicting the game currently, and a way to make playing more fun for all tanks, and probably everyone else as well.
Blizzard's talking the talk, and doing it well. It should be interesting to see if they can follow through with the implementation.