[SoftwareBug2.0]

It should be possible to use the new motor controllers to hold a position based on any sensors you want. However, you might have to run the control loop on the robot controller rather than on the motor controller. FYI, closed loop control is using sensor feeback to automatically control your output automatically. It's not essential that this happen in the motor controller itself. Even if you decide not to use the fancy features of the motor controllers there is at least one advantage I can think of for CAN: you won't run out of places to put PWM wires.

I don't know of anything that you want to do that shouldn't be possible in all three supported languages. Regarding speed, C++ should be the fastest, but any of them should be sufficiently fast for what you have described. A few things to consider when choosing a language:
1) For the first year with new hardware I would choose one of the three supported languages.
2) There is value in choosing something that at least one person (student or mentor) on your team already knows
3) Real computer science isn't done in a "graphical language".
4) While C++ is the most complex and powerful of the available languages its advantages won't become obvious until you're trying to do "advanced" things.

I don't think this project is going to force you to switch away from LabView but I would consider it if you have students how are interested to learn how to program.