Well just my experience with WC3/FT and other MMOs which all already have 'evil' Knights.
The funny thing is that so far in WOW, they have borrowed actually abilities MORE from older, rounded out MMOs than from their own WC3 (just look at how many skills have been moved around, forgotten, and made up) and have stuck to their WC3 roots more for Lore.
Death Knight seems to have already lent most of it's abilities to other classes, in one form or another, excluding of course the Animate Dead ability which is totally badass.
WC3's Death Coil ability does have the ability to heal undead, but it is quite simply a reverse "Holy Light" that the Paladin had, which now doesn't even do what the WC3 version did. And since Death Coil is already a Warlock Spell (and an important one at that), I doubt they'll be porting this over.
His Death Pact may actually be used just on his own Skeletons, as the ability is not portable from RTS (where it was a very good idea) to MMO (where it makes no sense.)
He does have an Aura, though. I'm curious to see where that goes, because this may be one way they bring out his 'DPS' side and his ability to change roles (much like Paladin.)