Unfortunately no progress yet, but this will hopefully change in the next weeks. By now we have given up on using the internal CAN controller: We have produced a device w/ the builtin CAN controller, but could not achieve reliable timings (for details, see, e.g.,
https://github.com/espressif/esp-idf/issues/12316). I'm afraid this is a limitation of the Espressif Silicon.
Our new design uses the 2518fd and a matching transceiver. I have yet to write a driver, but I'll start checking out the options soon. There are a few existing drivers, like the generic MCP driver library (for this you will only have to provide the SPI glue logic, which is not much). There's also a pretty comprehensive ESP32/Arduino driver which would have to be rewritten for ESP-IDF, if we were to use it. And also two 3rdparty drivers, one from SeeedStudio and one from another guy. Last but not least, there is the Linux driver which also is pretty comprehensive and has great code quality.
To achieve our reliable timing constraints, we will probably have to utilize the timestamped transmit buffers in the MC2518fd. I did not check yet whether any of these existing libraries support that.
Did you get any further with your project? Since this is getting off-topic, we might want to communicate out of this board. Drop me a mail via mickey (at) vanille.de, if you're interested on collaborating. I'd be fine if this would be an open source driver, but it's not a necessity for us.