It would be more nice to store the cache database under, because when backup of the settings and certificates the whole cache is also stored:
See Apple specification: https://developer.apple.com/library/mac/documentation/FileManagement/Conceptual/FileSystemProgrammingGuide/MacOSXDirectories/MacOSXDirectories.html
For systems who implement XDG Base Directory Specification it could be under:
If $XDG_CACHE_HOME is either not set or empty, a default equal to $HOME/.cache should be used.
See spec: http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html
It’s not really a cache though; deleting it has possibly significant negative effects.
Contains cached data that can be regenerated as needed. Apps should never rely on the existence of cache files
Yeah Syncthing’s home dir doesn’t match that. If anything, Syncthing requires