As cool as these Vic-20 and C64 clones are, I think it would be even awesomer to have a small MCU with HDMI booting into a micropython IDE. Of course, this mostly loses some luster when the hardware isn't as completely open/documented as the C64 (or later, Amiga and Atari ST). I guess an ESP32's openRtos is pretty open but also mighty complex, and there weren't dirt cheap completely open audio/video systems available last time I checked.
The RPI is great as well, but it's just much "bigger" and harder to fully understand (like you could understand a C64) for a young 'un.