A380-800r
A380 has been designed with a view to a stretch. The huge wing reference area. Compare A340-600HGW with A380-800! The wing area of A380 is almost twice that of A340-600. A340-600HGW MTOW is 380 t; at the same wing loading, A380 would have 750 t MTOW.
A380-800 now has 569 t. 590 t wing, landing gear and engine upgrades were prepared for A380-800F.
A380-900 needs modifications to fuselage and airports. A380-800R would have a slightly heavier empty weight and fuel burn than A380-800, but it would still be far cheaper than anything else, and it would have the extra range. Especially with limited payload. It would be the easiest and quickest A380 derivative. Note how much extra range 747-200 has compared to -100, or DC-10-30 compared to DC-10-10.