There is more space than you think below there! I had it in mind to cut around that rectangle with a "Dremmel". It needs to be cut out very carefully, as it would form the lid of the "storage compartment" Next, a suitable tray would need to be fabricated, to maximum depth. This would just drop into the opening, sitting on its own ~ 1cm lip. Now, the removed rectangle (which may need to be edged, either for strength or appearance), would be hinged at the rear to the "storage compartment" and there would be a "press-to-release/retain" catch at the front. This compartment would be flush with the top surface of the dash, the lid would be in the same material/finish and there would be no hinges/catch visible! I feel that certainly ones wallet and maybe even a sat-nav would go in that compartment! (if the sat-nav was secured to the underside of the lid, then that would make a very visible location for that device ..... just like the current A1?)
David