I could see having multiple single-use devices becoming a problem though too, and it doesn't seem to solve the "access" problem; the single purpose device could have its own vulnerabilities (hardware or software), so it just moves the target from one device to another, while (admittedly) limiting its scope of impact.

I'm also not sure the market would like it either, considering that the smartphone has wholly replaced many single-purpose devices (camera, GPS, calculator, etc.). The convenience factor may outweigh the security factor for many.