There is no port that I'm aware of. But I have interest in the BL702 - and, indeed, other Bouffalo Lab chips, particularly the BL808. The BL808 is used in the Pine Ox64 and the Sipeed M1s and the the BL702 is used in the Sipeed M0sense.

Bouffalo Labs provide the bl_mcu_sdk which appears to be reasonably well structured and supported, though still somewhat in flux. There are some question marks around their radio control; it seems that firmware blobs may be required for BLE and Wifi, though there's no official word yet. However, most other core micro features seem more mature.

Creating a MicroPython port takes significant effort - you have to spend a lot of time learning the manufacturer's SDK. But I think the Bouffalo Labs range of micros would an excellent platform to run MicroPython on.

Bare-metal, following the Porting MicroPython documentation would be my approach.

First milestone would be to get just enough of the port together so that the REPL can be accessed over a UART (or USB CDC if it's not too difficult). The examples folder contains a lot of useful guidance. After the REPL is available, start adding Pins and the other peripherals.

All of the ports are - by nature - quite different, but I would suggest looking to the rp2 port for inspiration, since it's one of the most recent, quite clean and relatively straightforward (particularly since it covers just one micro).