Check my new project, the Isetta TTL computer !  It will be a single board TTL computer with video output, that can run 6502 programs and also Z80 programs at a good speed ! It is expected to run Apple ][, ZX Spectrum and Commodore 64 programs with only minor changes. The sprites in the Commodore will be a real brain breaker, and although the microcode will will be able to transfer one pixel per cycle to the video RAM (in a small unrolled loop), it is unsure if that will succeed.