I want to easily hide certain personal images that I don't want just anyone to see. I am still on the search for an Apple Aperture replacement, and PMP is the closest that I have been able to find. But using it as a DAM for personal content requires me to hide sensitive images. Apple Photos has a global configuration that toggles hiding of images, and with Apple Aperture, I was able to create smart albums that could hide certain (hierarchical) keywords.
One potential interesting way to implement this in PMP might be to move a selected image to another catalog, but while retaining the same relative directory structure.
If it were me, that's how I'd approach it. Put the sensitive images in a wholly separate catalog so you can turn them off when talking with clients.
On a side note, we are looking at creating smart collections. I'm not sure it would work for what you're proposing, though.