Would be cooler if it were a 6128PLUS (or even a 6512PLUS) instead of a GX "064"...
GX4000 shouldn't be that difficult to implement, as it is a simple Z80 machine... well, the ASIC can be tricky and as it was more a keyboard-less computer, it had a large amount of RAM compared to most other 8 bit consoles or even 16 bit consoles.