My wife is a digital artist and has a Macbook pro, iPhone, and iPad, and I am constantly having to clear disk space from the Macbook due to all of the selfies, snaps, cat pictures, and legitimate photos that she takes constantly. I know I am not alone; these days, cameras are ubiquitous and the Apple product family has some of the best camera hardware and software, and the platform is widely used for digital art.
Her Macbook has 256GB of storage, which is always nearly full; I run a cleaner on it periodically, and have her delete silly pictures she doesn't need, but we shouldn't have to deal with this - non-mac laptops can ship with far more space, and even the current (2017) most expensive Macbook only has 512GB of storage. If I could tape a 1T usb stick inside the case, I would.
I am looking for strategies to deal with this, other than enabling photo compression/resizing on the macbook (she needs to edit her legit photos).
Her usage pattern is a single Photos library that is replicated with her iCloud account, which is fed with images from all of her devices.
iCloud clearly isn't cutting it, as it's an "all or nothing" proposition - I can't segment the library and only replicate certain types of pictures/directories to her other devices.
I am open to anything, and willing to pay for a solution if one exists. I have a large NAS in the home, but she frequently works on-the-go.