Has anyone tried it?
From what I see, making a stamp should be the first step. After that, a guardian (or use existing one), conquer condition, tactical map (make or use) in <WildlandsType InternalName="xxx">.
Wildlands as faction already exist in CoreRaceConfigs as: <RaceConfig InternalName="WildlandsPlayer">
Is there something more to it that I don't see?