If you're installing games or parts of them to the internal flash (assuming Nintendo doesn't include a hard drive) they aren't going to load substantially faster off a flash "cartridge" for anyone to give a shit, especially when the third-parties are already designing their game to stream with the optical drives of the Xbone and PS4 in mind. This isn't like the double speed CD-ROM of the PS1* vs. N64 here. Plus the other two consoles have hard drives to cache on. (And especially if the textures are one-fourth the size...I mean, a lot of Wii games didn't seem like they had any loading times vs. 360 comparatively.)
Remember when just installing to a HD broke Halo 3 or whatever it was because of the stream timings? And increased the load times in a bunch of other games.
It looks like a Flash ROM of 32GB costs around $2 per chip, that's surely more expensive than a disc.
spoiler (click to show/hide)
And both are more expensive than a code on a piece of paper in the box.
*~150-300 KB/sec
