Flightglobal has a new take on what is going on with the A350-1000. Contrary to Scott Hamilton, Max Kingsley-Jones thinks that the wing would be part of the design change, thus getting larger. This could indicate two things:
1. The Thrust/Weight-Ratio could get down without sacrificing runway performance as the larger wing would provide more lift. In other words, the MTOW could be lifted more than the ~5% gain in takeoff thrust, enabling the aircraft to carry more payload (especially cargo) over the reportedly new design range of 8500nm.
2. The investment for a larger wing and a "new" engine would make more sense, if another type would be added to the A350 family - call it the A350-1100 for now. With a further stretch of 4m it would have a fuselage length of roughly 80m, representing the ultimate stretch and would be a real B777-300ER competitor in terms of passenger capacity. The question then only is, if the range of the -1100 would be limited to 8000nm, comparable to the B777-300ER range, or if the -1100 would also get a range suitable for LAX-DXB (I now think that the 8500nm should work in >90% of the time for that route). If so, the "new" engine should really be a "new" engine - not just with an enlarged core, but also with a larger fan, as the thrust requirement would be more in the range of 105klbf. That would have implications to the basic design of the aircraft, especially the length of the undercarriage.
So Airbus could end up with the sub-families fo the A350 - the -900 and the -800 on the lower end and the -1000 and the -1100 on the upper end, very much comparable with the A340.
But again - until June 18 all is about speculation! But that's the fun with it...