black wolves are tameable just like normal wolves they spawn on top of grass at night in forest biomes. to tame them right click with a bone just like normal wolves. but don't attack them or they will attack you.
Jeb tweeted about this a long time ago. Since we now have different variants of cats, it can be reasonably assumed they are able to make variants of wolves now, and might do so in the feature.
This suggestion isn't very urgent however.