If you're that worried about losing the ability to load games from an external hard drive, just buy a Wode. It fully emulates the Wii's optical drive and is oblivious to any updates Nintendo does to the console. That's what I use and it's amazing, it even rips your discs to the hard drive for you. My kids haven't had to touch a game DVD in months. WODE
I assume that any of these 3D screen technologies are unable to switch from landscape to portrait without losing either the 3D effect or the picture altogether. That is assuming also that the 3DS will have two unique screens. This may hurt the DS/DSi backwards compatibily aspect. It could also be a single screen device where the screen would be virtually split in two and rotated to portrait for DS/DSi games.