Eric,
From a production standpoint, I would never start using a new release of Maya for production. Too many issues, bugs, etc. creating headaches, lost time, and missed deadlines. I recently just switched to 2016 from 2014 (comPLETEly skipping 2015) and really blew a job (no jokes, please) due to some unexpected things that were changed/added in Maya and Mental Ray. I would have been MUCH better off sticking with 2014 and my knowledge and expectations of the software. New modeling tools and the COLOR MANAGEMENT system were a GREAT improvement over 2014 and lured me into thinking it would be all roses. Wrong, wrong, wrong. MR Satellite does NOT work with the color management system, the Parallel Evaluation mode messed me up big time (being ON by default), and various other problems. And this was service pack 5. Had I spent some time reading the documentation, I might have learned of the Parallel Evaluation mode. The MR Satellite problem was documented in 2015, but was not in 2016.
As a teacher, I would suspect that a certain comfort level with the software is a #1 priority as you don't want to be caught off guard in the middle of class with something that worked as expected in 2016 but now was buggy or different in 2017. 2016 (and 2016.5) are fairly stable now, but only after 6 service packs.
I would continue to teach Maya 2016 in the Fall/Spring semester. You know MR, so trying to learn Arnold whilst teaching it seems like a doomed proposition. Give nVidia time to catch up and see what they have to offer in terms of educational licensing.
We're moving into new territory here. There are SO many renderers available and I think it's great that Maya is working towards an open rendering API. It took SO many years to integrate MR into Maya, yet it never really seemed truely a part of Maya even to this day. I think we will see schools such as yours adding RENDERING classes, where students are introduced to many different rendering solutions. SO many studios use multiple DCC applications, combining the best that each package has to offer. Redshift licenses cover multiple applications with one license, so working in Maya AND Houdini AND C4D is becoming more common. Teaching students across multiple applications AND multiple renderers will become the norm.
Good point about Macs not having nVidia support. So many renderers are moving to GPU rendering, including nVidia with MR. Hmmm....