Consider using i Cloud to sync specific photos from your i Photo libraries.The i Cloud service is available on the most recent versions of OS X and i Photo; the option may not be available for Macs running older software.I have a client who is having a lot of trouble managing his photos.He has multiple copies in multiple Aperture and i Photo libraries, imports from old PCs, etc.
In addition to content writing, Poland is also a fiction writer.
One quick note: Before you migrate all of your existing photos into Photos for OS X, make sure you have enough i Cloud storage space if you want to take advantage of i Cloud Photo Library, which syncs your images across al of your devices.
With i Cloud Photo Library turned on in the Photos app, all of your images will be uploaded to the cloud, which does eat up your i Cloud storage space.
What I'm looking for is a piece of software for OS X that can grab all these photos and reorganize them by EXIF data, say into YYYY/YYYY-MM-DD/*.jpg, eliminating duplicates as it goes. @Michael Clark, Short answer is no (unless you want it : D).
In detail: it depends on how you implement the script.