I don't see a problem with cartridges personally. For starters, shorter load times. No need for installation. You can substitute a HDD for simply ever more potent, easily exchangeable, less weighty memory cards (which doesn't cost the Earth if they break (assuming Nintendo fixes its e-purchases systems and have proper accounts). Plus it makes it so not worth the effort trying to pirate games for it.
I think someone said it above. So crazy it could work. As for portable? Ehhh, I can see the appeal. As long as it's powerful enough. Maybe have dual graphics options? Games that can run decently in portable with set display options, and another for a docking station hooked up to a TV. How nice it would be to play Co-op right next to someone, without having to move an entire console?
Or do the whole direct input-wireless contol thing. World is growing more mobile. More people living in temporary residences. Even in family situations, easy mobility is a plus. More people having more flatmates sharing common resources. The demographics of videogaming are changing, makes sense videogaming consoles keep pace if they want to be seen as better options to mobiles.