FYI, community member Blakadder is tinkering with the Sonoff NSPanel Pro and he has ongoing documents the internal workings as he comes along so he continuously updates his webpage and YouTube videos about his findings and hacking progress, with the most recent updates being ADB access (i.e. rooted/unlocked) which among other things adds the option for sideload/sideloading support for loading custom Android apps and also to update WebView and more on the Sonoff NSPanel Pro.
Tip is follow Blakadder’s blog and check for updates as has had access to one for a while and looks like he keeps documenting updates on hacking it there: