I moved your question to a new topic, since it did not really fit in with the other thread where it was originally posted.
Now for the answer:
The most significant change affecting Carloop with the Gen3 is the microprocessor hardware.
Gen3 hardware use a Nordic nRF52840 microprocessor which has no built-in support for CANbus.
The existing Electron, Photon and RedbearDuo all use the ST micro STM32F205 microprocessor which does have built-in support for CANbus.
So, it is not at all a matter of stability, but a matter of using different hardware for the CAN interface and developing the lower-level firmware to support CANbus. I do not have any word from Carloop to indicate if they are or are not planning a Gen3 version of Carloop.
By the way, that CAN featherwing looks like it would do the hardware side okay. It is missing the OBD2 connector and I am not sure if it includes an automotive power regulator. It uses a MCP2515 CAN driver, which I think is an older version which may not support CAN-FD. Depending on your needs, it might be okay or you might want to look for something a bit more modern. It does not solve the lack of low-level firmware, so it is only a partial solution.