So I did a little more troubleshooting....
-Kobo Desktop (which I just installed) also does not connect to the device.
-I charged up my old Kindle. It mounts to the OS, but it too does not mount in Calibre with a similar error message
Spoiler:
Looking for devices...
USBDevice(busnum=20, devnum=35, vendor_id=0x1949, product_id=0x0004, bcd=0x0100, manufacturer=Amazon, product=Amazon Kindle, serial=G090G10XXXXXXXXX)
Detected possible device KINDLE2
Devices possibly connected: Kindle 2/3/4/Touch/PaperWhite/Voyage Device Interface,
Trying to open Kindle 2/3/4/Touch/PaperWhite/Voyage Device Interface ... failed
Opening of the following devices failed
<calibre.devices.kindle.driver.KINDLE2 object at 0x1100f88b0>
Traceback (most recent call last):
File "calibre/devices/usbms/device.py", line 718, in open
File "calibre/devices/usbms/device.py", line 408, in open_osx
calibre.devices.errors.DeviceError: Unable to detect the KINDLE2 mount point. Try rebooting.
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "calibre/devices/__init__.py", line 157, in debug
File "calibre/devices/usbms/device.py", line 721, in open
File "calibre/devices/usbms/device.py", line 408, in open_osx
calibre.devices.errors.DeviceError: Unable to detect the KINDLE2 mount point. Try rebooting.
I dropped a comment in the Apple forums regarding this issue.