I'm guessing you're unaware of the fact that retail 3DS games have digital download versions as well.
You can play New Super Mario Bros 2 on a game card, or a digital download from the SD card you know.
So hypothetically it may be entirely possible to get any 3DS rom to launch from the 3DS home menu, if it was properly hacked. A flashcard might be totally unnecessary.
Ah yeah didn't think of that, ah well. Well If the game is dumped from a card wouldn't there be checks to verify the card, where as a eShop game maybe has modified code to alter its intricacies... I really am guessing lol..