Awesome idea, I definitely might get one!
By tall Famicom carts do you just mean the longer ones, that are morre NES-sized? I'd guess that some games still won't be playable on a toaster NES. Looking at the video, I don't see how this would make Jajamaru Ninja Daisakusen or Jajamaru Gekimaden fit into the system, for example; those carts are too thick, can't get into the toaster when connected to a converter cart. Fortunately I also have a toploader, but I hate its awful-quality video output...