I have been working on this project for sometime now. It started as a project to do just OTA support with API first approach. But then moved on to expose WoT api's that can be used by Things Gateway by mozilla. It also acts as a proxy to work with other controllers.

Currently supports Serial and TCP connection. MQTT support is in pipeline.

UI for firmware management is still in progress.

The project is open source and can be found here. Written completely in Rust Lang. Still at early stage. Feedbacks welcome.

Screenshots of Integration with Things Gateway is attached

I have been working on a project to do the FOTA through API. It is in workable state now. It can't be run on ESP, but you can run it on a raspberry or any linux/unix system.
Let me know if you need more help in using this project.

https://github.com/tsathishkumar/MySController-rs

@alowhum Will add the deb package for raspbian soon.