We are creating AEM form based on our XSD schema and we found that xsd schema elements (like xs:string, xs:date) are mapping beautifully to OOTB form components when dragging and dropping from content finder, ex:. xs:string to Text box components.
There is alternate way to enable custom widget via guideBridge using css selector (which should returns field for which you want to enable the custom widget) at template level.
If you still want the XSD being mapped to custom AF component on 6.0, unfortunately that's not supported right now. You would to get in touch with Adobe Support to log enhancement request for that.