Does Photos.app support a watch directory? Is it possible for Photos to automatically include all files in a given directory as part of its Library? Picasa, for example, offers this.

I have a folder on my computer that is automatically synced to other devices via an online service (e.g. Dropbox, OneDrive, etc). Although I can manually import those files into Photos, that requires performing the import every time new files are added to that directory.

I have tried creating a new Photos library (holding down Option on launch) in the directory mentioned earlier to see if it might magically add all the files there, but that has no effect.
Photos does not currently support a watch directory - meaning that all photos have to be imported manually (by dragging and dropping onto the Photos window or File > Import...) or via iCloud Photo Library or My Photo Stream.