For some time, the ebay seller zzapmort has been selling hardware with built in mechanical keyboards that uses the Raspberry Pi Pico to run a Spectrum emulator. I recently bought one of these and ported the ZX80 / ZX81 pico emulator (https://github.com/ikjordan/picozx81) to it.
There is now a listing on ebay for hardware that supports ZX80, ZX81 and ZX Spectrum emulators. Search for "zx81 pico". In the next few weeks I hope to port picozx81 to some of the other hardware on sale. I quite like the thought of a Pico in a converted ZX-Spectrum case running as a ZX81
Full disclosure: I've put together the picozx81 emulator, but I do not profit from any sales of this hardware.