Not to burst that dream bubble hanging over your heads, but if you're gonna take the time to put that amount of memory into every device, why not just have it unlocked from day 1? I would be pissed off a year later if all of a sudden my 8 GB device that I've been struggling to figure out what stays on and what goes, suddenly has 16 GB that it had all along, ya know? But with cloud computing, you technically shouldn't need that much space, you should be able to access a lot off the cloud, but that depends on what apps we get and how soon.
And to touch on the Kindle App, I can't see a reason why this wouldn't be good for all involved, Sprint and Amazon have a good relationship and already are partnered with the actual Kindle device. The Pre will use the Amazon music store for direct downloads...add books to that shouldn't be difficult.