in 10 years (a lot less i guarantee) you will not need any card... in early psp and wii homebrews you required a game exploit, now what you need is to just shove something in the memory card, launch an exploit and install custom firmware to the device...
when psp could be hacked through a pandora battery, then people start to sell pre-made batteries with the hack ready
the ds only needed a r4 because there is no way to connect a standard memory like a sd card\memory stick or usb stick.. its possible to explot it via download play but its not praticall...
flashcarts only exist so someone can make money... if there was interest on the device we could run cfw\homebrew\roms easily like we do on other consoles... smea was just one guy, probably a young one with knowledge and free time and he enabled homebrew on the damn thing...
what makes you think that flashcarts will still be a thing in some years from now?