Yep, indeed, there isn’t a lot of detail about either handling datasets that don’t fit into memory and/or hybrid/scanline approaches. (There are some exercises that discuss how to extend the system to handle large amounts of texture map data, however.)
While those are definitely interesting topics, we didn’t include much about them since the system doesn’t have algorithms for that stuff implemented. So the good news about the approach we took in the book is that if we do discuss an algorithm, we also discuss how to implement it in great detail, down to the level of walking through complete source code that implements it. The bad news is that if we didn’t implement a particular algorithm, we don’t discuss it very much. And given the length already, we had to draw the line somewhere… 
Certainly we tried to include what we thought were the most interesting/appropriate topics for the focus of the book (physically-based rendering), but there are plenty of interesting things like the stuff you mention that would have been nice to include but aren’t in there for the above reasons…
-matt