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.
While Cert pinning is a good thing for online updates, allowing the user to flash a firmware on a local network and securing it by letting the user confirm it with a press of a button on the device would be a good idea to keep it protected, while still allowing people to freely use their devices.
It could be promoted officially for offline updates, while just letting it work with unsigned custom firmwares, if they don't want to officially support custom firmwares for their devices.
The easy support for custom firmwares, to allow it to be used without a third party online server was the main reason I used it and suggested it to other people, so finding out only the soldering version works now was a bummer.
I agree with Sillyfrog!
It would be great!