Been using ScriptedImporterEditor, and so far so good.. However, it would be nice for an OnSceneGUI to be called for it. There is OnInspectorGUI, but there is no OnSceneGUI (and no OnDrawGizmos/OnDrawGizmosSelected).
It's not for a GameObject it's for an asset, but need things to be drawn on the scene. I know it wouldn't really make sense but would be nice for my scenario. Instead for now I created a temporary MonoBehavior that has attached.
Not terribly important, but a 'would be nice' :)