My new project is a Cortex M3 based board. The plan is that this board will be compatible with the older PIC18F2550 based panel.
I think, the circuit is ready. The peripheries has extended with a temperature sensor (DS18B20), and some usefull parts i.e. battery connection, SPI connection for SD-card pinout, I2C connection for BME280 barometer panel, reset jumper, TPS3813 heartbeat circuit (not tested yet) and Blue Pill compatible SWD pinout and PC13 LED.
The firmware is not ready yet, but many features work: FreeRTOS based process management, LCD display, STM32 internal rtc, temperature sensor, PWM for display backlight, UART communication, heartbeat signal and 4 buttons handle. I have to write and implement the USB, I2C and SPI divers and peripheries.