Author’s note: I have quit playing WoW before patch 3.0.5. Warcraft-related content is no longer being updated, and information in this post may not reflect the live game any more.
Wowhead (no, I’m still not linking to them) put up a WWI-based talent calculator for DKs. From a quick survey, it appears Blizzard wants indeed not to typecast each talent tree to specific roles, as talents fit for tanking appear in all three.
The good news, though, without having a concrete idea of the impact in terms of gameplay, it does appear that by level 80, all important tanking talents across all three trees are speccable in one single build, and you may even pick up a couple of DPS-boosting talents while doing so.
Of course, in practice this approach changes little of substance compared to some cookie-cutter 0/49/12 (or variant thereof depending on progression) tankadin build of old, it only gives the illusion of variety. Still, from the current design perspective, it looks like tanking talents are at the lower tiers, while all three trees have some interesting DPS talents in the top tiers (once the tanking stuff has been taken care of).
EDIT post release: People interested in looking at what builds and trees are viable on live would be well advised to follow this Elitist Jerks discussion. The current finding is that while blood tanking doesn’t cut it, the jury is still out between frost and unholy. And that’s a good thing IMO.