It's been a long while since I last revisited this sorta discussion and I don't really remember too many details from back during the event and some Live Letters. That said, I do remember Yoshi had admitted they were first considering SAM as the new tank for Heavensward but later decided on DRK.

I get the feeling SAM would be our new DPS that'd share a slot in the PT with DRG as well as their "heavy armor" DPS gear. RDM I could easily see filling the "support" role that BRD and MCH do, but with their own obvious RDM spin on it. RDM has always been a supporter/buffer in all FF games that I've played. So, that'd leave BLU as... well, I suppose a tank if we're expecting a new tank job. I can and can't see it. I wasn't expecting to see DRK as a tank, so I don't really know what to expect going forward.