Seriously... Netflix is in the movie renting business why wouldn't they allow you to rent(stream) movies from them? If you want to rent or own the movie on an SD card though, you could get it from another source, or Netflix could use their (assumed) app on the 3DS to recognize when you have transfered a (DRM protected) movie to an SD card and not allow you to even stream another until the one you transferred is reinserted into the 3DS to be deleted by the app.
Also mobile TV is HUGE in Japan; with Nintendo being the first mobile with a 3D display they could easily also be the first to provide 3D mobile TV. With the mobile TV market in its infancy in the US this is another big chance for Nintendo as channels like ESPN have already launched 3D channels, and would definitely love to expand their new channels into the mobile market, getting them more viewers and thus more ad revenue. The 3DS, with enough internal storage could even offer DVR capabilities--although I imagine storing 3D programs would need a lot of space, so you would probably only be able to record 2D shows. I know that's asking a lot but when you look at how much companies like HTC and Apple are able to pack into really thin phones I'm expecting a lot from the clamshell 3DS which can afford to be thicker for ergonomic reasons and thus have more space for storage, processors, radios, etc.