This is idea ...
I get Espruino pico board + arduino headers and this is crazy MIX :-D
Because exist native DFU Micropython port for Espruino PICO you can run BOTH on same board of course you can program native STM32 code... and maybe exist STM32F4 Arduino core or .NET ????
Now in credit card shape
...There is lot of space for extra buttons ... headers .... etc ... oled, rtc, cr2032 battery RGB led, encoder, rf module or just simple card ??