I’m not familiar with ESP-NOW, but if there’s a Linux driver for it, there should be a way to use with Nerves with some work.

If there’s not a Linux ESP-NOW driver (I couldn’t find one on quick search), I’d make a wired connection between the RPi and one ESP32/ESP8266 and use that local ESP for communication with the sensor node ESPs. Bridging over the UART pins might not be bad if you don’t mind coming up with a communications protocol for your app.

One other solution which I am playing with is to use a CANBUS enabled carrier board with a RPI4 compute module that can talk to your ESP module. You can output CAN frames from your ESP (at least ESP32 Classic+) to communicate with your carrier board (which exposes CAN as network interface in linux). Might save you reinventing the wheel with a communication protocol and lean on something that is industry ready instead.

If you could get Linux running on ESP32 though, wouldn’t that mean you could potentially get Elixir/Nerves running on the ESP32 (with some effort?)… that would be cool and drop the cost of hardware for nerves implementations right down…