I recently got a (good!) 3D printer, and that combined with Claude has got me building lots of custom hardware devices using ESP32s.
I don't really see the value in a full-computer experience (which seems to be what most cyberdecks try to do - badly) but I can see utility in "sidecar"-style hardware, which is more akin to a phone app but with a better experience because of custom hardware.
For general compute they will lose to a laptop, but that isn't supposed to be their purpose. I think the best use cases require extra hardware that would make a laptop too bulky or awkward. For example a deck with a VNA, SDR, scope, and arbitrary waveform generator for field work with radio equipment. The traditional computer capabilities are sort of extra. Any sort of diagnostic "cart" with a dedicated computer and a bunch of test equipment could be a candidate for miniaturization.
I always wanted one of the tiny form factor laptops but during that period I had a specific need for a real non-usb hardware serial port and instead bought a laptop that actually had one which was very strange (2009 maybe?)
I don't really see the value in a full-computer experience (which seems to be what most cyberdecks try to do - badly) but I can see utility in "sidecar"-style hardware, which is more akin to a phone app but with a better experience because of custom hardware.