i think a good idea for a fantasy console would be something like: it's literally an emulated game boy, but running at a higher clock rate, and the emulator bypasses the built-in PPU and interprets the VRAM according to a different convention that would allow for (e.g.) higher resolution graphics
the benefit of this is that you could use all of the pre-existing tool chains for game boy dev, and keep all the crunchy constraints of an 8bit system, while having a display that doesn't make information design so difficult. also if you kept the clock speed somewhere in a reasonable range (12MHz?) you could even imagine an actual game boy processor at the center of a (non-emulated) system, if you had an external mcu/fpga that handled the new graphics convention
this line of thought brought to you by the realization i had earlier that there's really nothing stopping you from running a varvara machine with an emulated game boy CPU (instead of a uxn virtual machine) and i think that would be fun to try!