So in the process of building my warcraft armory app I came across an interesting tidbit of info. I was mapping the class id values to names, and I got the following map:

    WARRIOR(1, "Warrior"),
    PALADIN(2, "Paladin"),
    HUNTER(3, "Hunter"),
    ROGUE(4, "Rogue")
    PRIEST(5, "Priest"),
    DEATHKNIGHT(6, "DeathKnight"),
    SHAMAN(7, "Shaman"),
    MAGE(8, "Mage"),
    WARLOCK(9, "Warlock"),
    DRUID(11, "Druid");

Now, if you are a programmer and you have to write an enum, you will pick sequential numbers. Death Knights which appeared in 2008 have id 6. They have id 6 because they were picked from the beginning and later removed from the initial vanilla wow launch. For the first few years, the id 6 was probably empty and nobody parsing armory xml knew what the name associated with it was. Come 2008 we now know.

On to the question... what lies behind door number 10? :) It's surely something picked from the beginning as druid comes at 11. Also, who would pick 11 for anything, 12 is such a nicer number. Is there anything hidden behind door number 12? I'm almost sure the name and the idea behind the missing classes is there, and there's probably good reason why they are not implemented.