For post-7.1.GA consideration:

General/Structural issues:

• I think that the Elytron vs. legacy subsystem difference needs to be explained in the overview/introduction (i.e. near the beginning of the book). Do we have a standard topic for this? It probably would be useful to mention in multiple guides regarding security.
• The Elytron chapter could use some information at the start detailing what it includes/covers. It looks like it mainly handles different authentication configurations (perhaps it could list the different options).
• Same as the above point for the Legacy subsystem chapter.
• The elytron and legacy chapters seem to cover similar content, but the order of the authentication types and their titles are different.
  e.g. Elytron: "Configure Authentication with a Properties File-Based Identity Store" vs.
  Legacy: "Configure a Security Domain to use a Properties File"
  Unless there is a reason for the different order and naming, they should be the same.

Other smaller issues:

• The use of italics to introduce a new term to the user? I'm not a fan of this, and I don't think it is consistent with other EAP books.
• Login module names should be in backticks (also affects Login Module Reference book). In most cases they are unformatted, others they are italacised. They should be made consistent.