There will be no diesel M3 for sure, but a high performance diesel F30 is more than likely. I don't think we will see the tri-turbo N57 (50d) being dropped into the F30 because there will be physically no room for it + xDrive! 381hp and 740NM cannot be safely transmitted to the road (as good as the DSC is) through a RWD on 255's unless you really know what you're doing. It's the torque more than anything. It's a squeeze to fit the 50d and xDrive into the F10 as it is because they do not have the room to switch it to a right hand drive version for a market such as the UK who drive on the correct side of the road, so I will not see it
. A 335d which is now producing 313hp in its most potent form in the F10/F11 will be definitely on the cards sooner or later and maybe an "M40d" will be introduced but anymore than 630NM in a RWD may warrant the xDrive, so we're back to the drawing board.
The 8spd ZF will need to be toughened up too from 8HP70 to 8HP90 if it goes over 700NM of diesel torque which will probably add cost, if it doesn't take up more room and add weight as well, but I'm not sure on that. I do know that the 8HP70 weighs 90kg but that is my knowledge exhausted!
I have attached two pictures of the 8HP70 and 8HP90 which can handle 700NM and 1000NM diesel torque respectively. The 6MT will disintegrate, as I believe (but cannot confirm) that its limit is 560NM.