4GB would fit a lot of hypertext. Now, if they could create a "teacher's" version with 16GB, you could have multicast multimedia sharing over wifi, which would enable classrooms to use video content with only a fraction of expense in Flash RAM.
Another option is to use p2p as a storage mechanism. And since the storage capacity would be bigger, it could enable personalized videos.
Sure, if you could ensure enough redundancy. But I wouldn't have enough confidence in such a system to preclude failure in the event of too many students absent.
HTML is the future of textbooks.
I'm not advocating video over HTML. I'm suggesting a cost effective way of providing video when it's needed.