I'm one of the maintainers of the opensource project https://github.com/mirko/SonOTA , however with the latest release there appears to be certificate pinning (or similar) happening. This means that users can only upgrade the firmware in the Sonoff devices if they open it up, and solder in headers.
Using this OTA method users could get all of the benefits of an open platform, without the the need to open up the device and solder etc.
This could be done in a secure manner, just allow a manual OTA update in AP mode. Then it would just require physical access on the stock firmware. Or just add MQTT with homie or homeassistant out of the box without requiring an internet connection and I wouldn't even need a custom firmware.
Hey, same as everybody else... I'm starting with home automation in my city and i need OTA functionality!