Having had a look at the pictures - maybe the large black area is covering/protecting a ribbon cable between the keyboard and the electronics in the 'Lid'
Gunnar, ref your remark "The big panel may look great for those of us who like aeroplanes and spaceships" I don't think there are many more controls etc than there are on the KN6000 and the hinged lift-up panel is not new (Yamaha PSR6100 many moons ago)