You do know that the MSX computers were Z80 machines not 6502 right?
Who wants cartridge slot loading computers or consoles these days? Games and other software comes in the form of files you download from the internet in the 21st century.
Are you thinking of some kind of hybrid machine that is compatible with MSX, C64, NES and Apple II all at the same time with a single hardware configuration and OS? If you are then good luck with that because I'm no expert on these various platforms but I strongly suspect the inherent incompatibilities are enormous and insurmountable.
The differences between the various dialects of 8 bit BASICs often reflect the differences in the architectures, operating systems and expansion options. The BASIC interpreter and OS takes up a large chunk of the address space on these machines for the ROM image. A hybrid version would inevitably be much larger.
Does anybody actually want an MSX, C64, NES, Apple II hybrid computer apart from yourself AmigaClassicRule? Wouldn't most people prefer to use emulators of those machines or perhaps FPGA implementations on an MCC216, Chameleon 64 or Replay?