Don't really want to get into it but arcane knight would have taken the place of berserker. As far as I can tell a 17th class would be unworkable in 3.0 (at the very least they could never have more than 5 max HP before items and buffs, which would be a bit hard to balance things around). Second, there's totally room for a 16th class right now in my opinion; they'd just take up a rogue/wizard spot in raids, which most raids seem to have 3 or 4 of already. Arcane knights would have filled the same big DPS role..