I have looked at the Weact Blue Pill Plus, and think it would make a 
nice, low-cost micropython system.

The WeAct BluePill+ pcbs have a GD32F303CCT6 (256 kbyte flash, 48 kbyte 
ram).
On the front of the board, remove the GD32F303CCT6 and put a 
GD32F303CGT6 processors (1024 kbyte flash, 96 kbyte ram) in place.
On the back of the WeAct BluePill+ solder a W25Q64JVSSIQ (4 mbyte) or 
W25Q128JVSIQ (8mbyte) flash and a 100n 0402 capacitor
This way you have a small system with 1mbyte flash, 96kbyte ram, and an 
external spi flash of 8 mbyte for a filesystem.
This is sufficient to run micropython.

Two problems:
- The GD32F303 processor can do quad spi, the W25Q128 spi flash can do 
quad spi, but unfortunately the WeAct BluePill+ board connects the flash 
as spi, not as quad spi.

- The GD32F303 devices have some small differences wrt to the STM32, 
that mean you cannot just compile micropython for STM32F4 and hope it 
will work on GD32F303. Gigadevice provides CMSIS and HAL, but what is 
missing is software that is known to run on this processor.

Do you know of anything (micropython, lua, ...) with a GD32 port?