i was trying to code it but i'm not so good at coding so i can't. but my aproach was to use the game at windowed full screen mode and use a function to execute the desire emulator on window mode and force it on top of the game window (for example snex9 for snes) from the mod folder (u have to put the rom and the emulator in the mod folder, and name the rom the same as the cartridge (x example SNES_Cartridge_Mana.src) and a function to detect wich cartridge you have to select the same rom as the cartridge. i didn't manage to execute the emulator nor the rom i had, its a shame bcs i think it is possible. srry my bad english

Possible? probably
But don't think that's the best idea even tho it sounds cool. Would requiring to run things outside of the game which would be too much for most people. Bunch of legal stuff too.
I am working on a different mod that will do something similar but on a much smaller scale.

Well then i will wait till u make that mod, it sound pretty good