Not to bring down your point, but there are repros with switches on them to load different roms, or different versions of a game, so it is still possible, though certainly more costly, since those would need to be custom made.
I'm not advocating repros though, even if I do own and enjoy mine. I'd recommend a flash cart over them any day, as that would let you load translated/original/fanmade/whatever rom you want on original hardware. Again, though, a handmade cart by some dude, and I can see that not having the appeal that some might look for in handling and enjoying actual factory-made original carts.
But that doesn't make moot the advantages of the Retron 5, it really just depends on what the individual wants. Original hardware isn't going to matter much for some games, and it does for others, same with original carts vs roms or repros.

