I am getting in my own M.2 case tomorrow, but having done some research prior, I will share what I know. Firstly, according to this, you can Control LibreELEC via an IR remote using LIRC, while it is on. However, I am not sure about Powering ON specifically, as this requires that the IR receiver be powered even when the RPi is not powered on. This mainly depends on how the Argon40 team wired their board. An alternative that I know works is the RemotePi Board, since this is exactly what it's intended for. Unfortunately, the RemotePi board doesn't fit this case. Anyways, I will know more when I get the case in.
