How would Necromancer and Witch Doctor classes work, in order to make Demon Hunters they had to butcher Demonology Warlocks, remove Metamorphosis and change the way they function completely, now for Necromancer and Witch Doctor they will have to do the same for Unholy Death Knights and Restoration Shamans - if you can find an alternate way you can say it.
For Necromancers - they have to remove death coil from unholy dks because its the main ability of necromancer (they can replace it with an unholy version of howling blast for dks) and they also have to remove the zombie minions apart from Val'Kyr and find an alternate way for how they will function (maybe Val'Kyr can be their main minion).
For Witch Doctors - they have to remove healing ward & chain heal from restoration shamans (i am not sure if shamans acctualy have the healing ward ability) because these 2 are the main spells of witch doctors, chain heal can just be replaced with a different name/visuals for shamans so it's ok, and they also have to remove the ''hex'' ability.
I personaly think that Witch Doctor class is possible because they don't have to change the entire way that restoration shamans work but only removing 2-3 abilities where the 1 can be replaced with a similar one anyway but for necromancers i think it will be harder to work through this.