I’m not sure the indirection would make sense, as -inotify doesn’t have a GUI etc.
It’s an integer of seconds, so 231-1 or 263-1 depending on platform, both of which should be sufficient for the foreseeable future.
I don’t think any of this has anything to do with unmounting filesystems. Watching a file/directory (like -inotify does) means having an open file descriptor on it, which prevents unmounting it.
When this gets integrated into Syncthing I expect the proper action is to pause the folder in Syncthing to be able to unmount it. Or, to not run inotify on removable disks.