Nothing official from SE from what I have seen, and not heard of anyone starting fresh unlocking the job yet. But multiple unofficial sources (which admittedly may be feeding off of each other
) have MRD as the designated subclass for the unlock.
Once I'm through my GC choice & got my chocobo, I plan to level both to 15 anyway (along with MNR, BTN and a Hand class to 19 for materia). MRD because a) I enjoyed it in P3, b) tanks are always good for DF and c) Mercy Stroke is @ 26. PGL was going to 12 for Internal Release, so it's not far from there.