[I have submitted the following issue but am posting here for the sake of discussion]
Pharo is used by software developers, and software developers depend on packages. Therefore I believe that one of the first things a new Pharo user will want to do is install packages written by others. But Pharo By Example contains no mention of the ConfigurationOfXYZ method of installing packages (and does not mention the configuration browser -- an awesome tool for new users to get excited about what is out there). You could introduce these topics without getting too deep into Metacello, but...
I also think Metacello should be introduced fairly early. Any application will almost certainly have dependencies and it is important to be able to load your application into a fresh image. Metacello is essential for this, so it is essential for Pharo.
Chapter 8 could probably be expanded to include these topics, which are more fundamental than Morphic or Seaside. Note that the Seaside chapter recommends installing an old one-click image! This is a great chance to use Configurations.
What do you think of this idea? And yes, I realize I can contribute this myself, but I currently decline the commitment.
Lyn