There was a company years ago that offered at least a USB based cartridge slot. It looked like one of those hard drive docks. I don't remember what happened to it, I believe it supported the original NES cartridges, if not more than one console. I remember it being pricey for the time though.

I agree, they could make bank offering that but they won't because that supports after market sellers, not Nintendo or the maker of the games themselves in any way.

Sega, Nintendo, Atari even, make more money reselling us digital copies bundled with an emulator at $7.95+ per game than they ever would offering a simple, affordable, option like a USB cart adapter. They would probably lock up something like that in legal limbo just to be jerks about it.