RSAdam hinted they might be looking into doing the SD70M in this thread:
http://railworksamerica.com/forum/viewtopic.php?f=9&t=3122As far as I know however, nothing more has come out of it. Trainguy76 was working on an SD70M:
http://railworksamerica.com/forum/viewtopic.php?f=31&t=1578&start=105But there hasn't been an update on it in months so I can only guess it's either stalled or been abandoned.
As for the SD70M-2, we already have one that comes with the SD70 Volume 2 pack. The only real difference between an SD70ACe and an SD70M-2 are the ACe uses AC traction motors and the M-2 uses DC traction motors. Externally, they look pretty much the same.