This is a late reply, but by default, Photos stores images inside a "Photos.photolibrary" package, which is just a special folder. Inside this, all your masters are contained in a "Masters" folder which is arranges every photo in a sub-directory hierarchy of:
year > month > day > day-timestamp
You could potentially symlink this folder knowing it'd have to be a one-way 'cloud' implementation because I would have to imagine modifications to anything inside here would corrupt the Photos.app library org.
Alternatively, you do not have to import photos into Photos' library package and have them as referenced. These referenced files could be in Dropbox/S3-sync'd folder/SAN etc in whatever org you want... same deal though if you modify location/attributes outside of Photos.app, it may mess things up.
year > month > day > day-timestamp
You could potentially symlink this folder knowing it'd have to be a one-way 'cloud' implementation because I would have to imagine modifications to anything inside here would corrupt the Photos.app library org.
Alternatively, you do not have to import photos into Photos' library package and have them as referenced. These referenced files could be in Dropbox/S3-sync'd folder/SAN etc in whatever org you want... same deal though if you modify location/attributes outside of Photos.app, it may mess things up.