We have been told by Blizzard Dev Dean Ayala that if the Demon Hunter concept is successful and popular with the community that we will get more new classes.
Like Demon Druid, Demon Mage, Demon Paladin, Demon Priest, Demon Rogue, Demon Shaman, Demon Warlock and Demon Warrior.
I hope it successed. I cant wait for all the other class. And they said if all the other classes success, they will create Demon Demon Hunter.