There are some arcade loaders that work sort of like this. The Naomi loader uses as raspberry pi and some custom hardware to hook into a Naomi motherboard and load the data into it as if it were a native daughterboard and you can press buttons on the RPi to switch games. Likewise, the FDSStick and FDSEmu work similarly in that they hook in-line with a real FDS RAM adapter and just pass the disk's data to it as if it were a real drive, which makes for perfect audio (something that's a bit lacking on the N8).
My biggest problem with this approach for NES carts, though, is that you would have to sacrifice donor hardware, i.e. desoldering chips from actual carts and replacing them with the loader. Besides, the N8's MMC3 mapper emulation seems to be quite solid (it passes all of the MMC3 test ROMs I've thrown at it), and the only mappers it really has issues with are the one VRC7 game and a small handful of obscure MMC5 games (Castlevania 3, the one "big" MMC5 game, works well). In either case, you'll have to destroy an already rare and expensive game to produce the multicart.
There are folks that produce SuperFX multicarts that run all of the SFX games (including Star Fox 2) off of a single cart, which is really cool and a lot of SD2SNES owners have purchased these since that flash cart doesn't emulate the SFX chip. However, each multicart requires sacrificing a copy of Doom or Stunt Race FX, which are cheap and relatively plentiful right now but won't be forever.