One ideal solution would be to have an automated card duplicator, but without a notebook, it would be hard to verify the copies, and even being able to duplicate the cards becomes a hassle when your camera uses. LM is also working with systems that use CFexpress, an NVMe storage format that isn't compatible with much other than high end cameras. He could write everything out to slower drives, but that's all the longer he has to wait before he can get back to using his card or his camera.
Something like an updated Gnarbox could be built around a CFexpress reader, an SBC and just enough Linux to read port one and spit it out on port 2, but I suspect that the licensing to get USB 4/CFexpress support would wind up making for a device that costs $laptop in the first place. An Odroid H3 might be a place to start, since it at least has NMVe support.