Interesting choice of travel...
Since there is a CPLD or FPGA sitting there, it would presumably be possible to create a ZX80/81/Spectrum switchable in the same case?
1. Switching regulator
2. Internal microfan... not needed modern components
3. Support for ZX81/80 on CPLD as someone mentioned...
4. Spectrum to ZX81 bus convertor is there one? I want to run Z'pand.