I actually believe its more possible of THM becoming DRK than MRD. But if they really add class combos for jobs (i hope so), i'd like to see these options:

MRD + THM = DRK. Focused in fighting while taking power from dead enemies. For DRK i already even suggested an WS that would be the coolest thing in a game where you can violate dead corpses like you do here...an AoE WS that deal tremendous damage but that can only used in dead monsters...can you see the beauty of such mechanic? You actually would be using dead adds to deal damage to the other targets!

MRD + CON = Viking. If you think PLD is the melee version of WHM and DRK is the melee version of sage, Viking is the melee version of BLM. Would be extremely fun to have a bulky BLM swinging an axe enhanced with elemental power and nuking if the target is too far.

MRD + GLA = Temple Knight. That dude frrom FFT...the one that uses a bigass sword and is focused in incapacitating targets.

MRD + PGL = Fighter. That classic job from FFTA serie. Specialized in high risk, high return battle.

MRD + LNC = Who knows...they both don't really fit any other class...could be templar, but it has little to do with MRD...templar would be more like LNC + Time mage/THM

MRD + ARC = Idk either...MRD + Musketeer could easly be soldier, with a gunblade, or cannoneer with a heavy bazooka-like weapon for heavy long range AoE damage.