I think we all expect Nintendo to redesign 3DS at least once. While I'm more than satisfied with the DSi, I was pretty pissed when XL was announced less than 6 months later. I don't actually treat my handhelds as portable on-the-go devices (I know, it's backwards... whatever). They're all consoles to me because I only play videogames at home or at a friend's house. I justify their existence as long as they have games I want to play.
Anyway, I think a 3DS XL is a given. The final 3DS model doesn't really lend itself for a more compact redesign as it's pretty packed as is so a model with larger screens seems like the most likely scenario. However, my question is: do you think Nintendo would not only increase the screen size, but the screen resolution as well, something they didn't do with the DSi or XL? This would undoubtedly drive the price up even more, but the games would sure look prettier. Nintendo would probably also have to include better cameras as pictures would look like crap on anything but the 3DS'sesses native resolution.
I think it's an interesting concept and certainly a possibility (I'm sure Nintendo thought about increasing the resolution for the DSi XL). I'm leaning toward "very slim chance of happening," but honestly, I'd totally buy it.