While I don't own a Switch so i'm not up and up on the security end of things with it (outside of following the scene a bit out of interest), I imagine, developing a flashcart would be fruitless, as Nintendo would likely find a way to block it with an update even if you found a way to get it to boot etc. I mean maybe if the flashcart has its own upgradable firmware you could play a game of cat and mouse and release new updates every time Nintendo does to keep it functional, but that seems like an awful lot of work when CFW already exists that readily available. Not trying ti discourage you in anyway just giving my 2 cents.
Would it be cool to see a flashcart on the Switch? yes of course it would be, would it be worth all the effort though when there's already solutions readily available (although on newer consoles, soldering is required but still)? Idk.