1) Syncthing "middleware": don't just sync files between devices, but specify logic of what should happen when a device "sends" or "receives" the file.
E.g: NAS stores music files in high-res MP3 or FLAC, but you want (part of?) them in your phone as lower-res format.
It would be a good project for me to use and learn more of Go, and it would work well with what I had in mind when writing https://raphael.lullis.net/thinking-heads-are-not-in-the-clouds/
Just too big of a project for me to do it now.
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