What attracts you to Late Rome?

[Frank]

Does this mean that this is the only book in the series dealing with military history and that the others deal with other aspects of Roman life, or will there be other books taking military history on from 361?

Well, 284 to 361 is the interesting part. 8)
On the other side, I hope thats just a title. A book, which likes to describe and explain the transition of the imperial army, should start latest with Gallienus, and observe some measures of Septimus Severus and mention even actions as early as the reign of Marc Aurel.