How can I find out which photos need keywords in Apple Photos?

With iPhoto it was easy to create a smart folder that would identify photos with no keyword (Keyword = None) so I'd know they needed processing. Apple Photos does not appear to offer that same, highly useful, functionality. Is there any workaround that anyone can think of that would plug this gap in Apple Photos, please?

Using OS X 10.10.3 and iOS 8.3