Hi dlabun,
Did you see the pull request to add the SAMD51 CMSIS to Arduino CMSIS repository?
Yes I did. I guess it's likely that SAMD51 CMSIS files will be supported in the next version of the Arduino IDE, or maybe already are with the hourly builds.
For now I just got the SAMD51 files from the Adafruit's "ArduinoModule-CMSIS-Atmel" repo on Github.
By the way, I've got the boards manager going...
