I remember Yoshi talking about multiple jobs from one class. The point, if I remember correctly, the jobs were going to be like specializations, kind talent trees in other mmos. I see no reason each class shouldn't have options.

Simple Examples
Gla
Tank -> Paladin
DPS -> Dark Knight

Pug
DPS -> Monk
Pet DPS -> Puppet Master

Ect.

Who doesn't love options?