Unless DNC is a tank, SAM is a DPS, and RDM a healer, which I pray it not...but who knows? The only thing we're missing in question is a healer job.
I am guessing that Sam will be a tank class this time around, for no other reason than it would almost single-handedly solve the lack of tanks and queue time problems the game is suffering from right now. That kind of silver bullet solution would be very appealing to the devs.