In the details, I mentioned the "utility socket" I plan to add to the device.

I'm trying to use only I2C modules and components inside the device. So, there are "a lot" of unused GPIOs.

I plan to use some of these remaining GPIOs in the utility socket :

• 3.3v
• GND
• UART Tx
• UART Rx
• I2C SDA
• I2C SCL
• ADC
• 1 digital pin
• GPIO 0
• Reset

It would allow using "slave modules" with the device, while GPIO 0 and Reset will allow to reprogram it.

For an example, I could plug a I2C Inertial Measurement Unit, or a Serial GPS.

I plan to also use AtTinys and Atmegas coupled with sensors/actuators, as I2C slave devices. This way, I could use some IO absent on the ESP8266 : SPI, hardware PWM, analog... Each slave device will have its own unique address, so the main device could identify it, and run the appropriate function.