Where does the current Roads to Aventure kickstarter for the Castles & Crusades rpg come into play within the D20 Wilderlands of High Fantasy?! If we start looking at the role of wizard guilds within the Wilderlands there is a strong connection to a supplement like the Adventurers Spellbook.
Within the Wilderlands & even to certain extent of the City State of the Invincible Overlord there isn't an Elminster Aumar, the Sage of Shadowdale, constantly waging his finger or wringing his hands at your PC's. The guilds are looser producing some devestatingly dangerous wizards. This is part of the charm of the Wilderlands of High Fantasy as a Sword & Sorcery setting. Its the setting that the players & the dungeon masters customize during play.
The new book looks like it will fit in the appendix N traditions of the Wilderlands of High Fantasy as a campaign setting that pulls highly from a rich tradition of being descended from Conan, Gor, Barsoom, Jondor, Pelucidar, and other early sources of fantasy including Tarzan of the Apes.
Many of the spells,artifacts, including many of the Wilderlands' gods and religions, etc. all fit within the context of Castles & Crusades. All of the classic Dungeons & Dragons elements are shared between the Wilderlands & the Castles & Crusades rpg system.