These are two really successful FCS programs that have long-standing stadium sellout streaks. Both have stadiums that are large enough for FBS (although the Fargo Dome would likely need to be expanded). Both would be the only FBS program in their state and region. Both programs are in a far better position to succeed than the last three additions to FBS: Georgia Southern, Liberty, and Coastal Carolina.
I strongly recommend a game at Washington stadium (Montana). It's a pretty cool environment on gameday, and totally unexpected. I've never been to an NDSU game, but I understand it's a very loud experience, 20k packed into that little shoe-box.
The biggest obstacle for both programs is getting to the 14 sport minimum.
As for the MWC, if TV revenue is the goal, Montana and NDSU don't bring anything to the table. So it's hard for me to envision this happening.