Thats right. I would love to see the assassin in the expansion pack.
Actually I came up with some other Ideas of archetypes based on the current character classes:
Barbarian + Witch Doctor > Druid
Demon Hunter + Monk > Assassin
Monk + Barbarian > Paladin
Wizard + Witch Doctor > Illusionist
Witch Doctor + Demon Hunter > Necromancer
Barbarian + Wizard > ?