Not a lawyer either, but:
> What if I take the design, print it, include the thing in a staged photo, and sell prints of the photo?
Probably fair use, provided the design wasn't the main focus of the photo, but merely part of the "set dressing."
> What if I skip the printing and use the design files as a basis for a rendered photo or animation?
> What if I print the design, then use a 3D scanner to recreate a file from the physical artifact?
Those questions are simpler - both scenarios would be derivative works of the original files, so covered by the license.
but are those derived works copyrightable? I don't think they are.
Copyright law forbids the creation of derivative works (excepting any region-specific fair-use rules) so you're only allowed to create them under the rights granted to you in the terms of the license - thus under this particular license you can't make commercial use of derivative works.
But is a physical item a derivative work of it's technical specifications?
If the design files qualify for copyright protections, then modifications to them would clearly be derivative works.
I don't think it is clear if the keyboard itself would be a derivative work, as it almost certainly can't be protected by copyright. This is what patents are for.