About a decade ago, I wrote a system of intermittently connected systems that would run independently and sync up to a central db, all using firebird (uuid custom type) and a few utilities that ran via C# (mono under suse). It worked surprisingly well for the purpose it was designed.

Firebird was definitely nice in terms of being able to utilize the same db from the local systems (embedded) to the centralized server (service mode). As you say, it could use some love, but some of that could be done via symlink and/or consistent structure (/var/firebird/db/*). I haven't even looked at it in a while, wonder how hard it would be to use with electron/node, may have to look.