Per Ika-chan’s Falcom News Express # 62:
There will be two Sora no Kiseki books released in Sept!
The Legend of Heroes Sora no Kiseki FC Scenario Book
The Legend of Heroes Sora no Kiseki FC/SC/3rd World Guidance Book
The Scenario Book is exactly how it sounds- the scenario for FC collected into one large volume.
The World Guidance Book is a collection of world data and organizations for the world of Sora no Kiseki. It is a fully detailed materials collection for the trilogy of games.
These will both be published by Softbank. The preorders for these books will open soon, and more details will be available in a few days.