I'd say not till 2050 because the A350, 777, 787 will continue to undergo efficiency improvements and any future models from A and B will only be even more frugal. The 380 would soldier on as is and the cost difference between operating it versus one of the twins will only widen. So till 2035ish sounds feasible.
I enjoyed ScottB's post. I agreed with everything but the 2050, but let me do details on what your 2035 is a good estimate in my opinion:
1. Evonomy of scale. All airframes that had long lives had enough opperating to generate great spare parts revenue (even if by relation to prior frames such as the MD-90). Trust me on airlines are unwilling to pay business jet economics ,(e.g. , a BR700 overhaul is twice as often as a CFM-56 and costs about 50% more or 3X per takeoff).
2. Continued improvements. New aircraft such as the A350, 779, or 787 are more software than hardware. New code reduces maintenance costs.
3. Four engines is four overhauls, weight, and drag. Since both engines have poor economy of scale, they will be the next V2500-D5 (shops abandon certificates at the first hint of a volume drop). You can forget about CMC PIPs for low volume engines.
4. Fuel burn per passenger. Never outstanding, the A35K and 779 set the new bar. As PIPs happen, the in production frames pull ahead (as already noted).
I see EK extending leases. But I doubt EK will fly the type past 2035. This isn't the 747 where a large cargo market is keeping all the wear parts in production. So do not expect anyone besides BA and EK to find a quantity of used examples of interest.
I'm sad. I've posted here for years of the potential of a stretch. But if I'm rational, it is obvious the resources the A380 consumed hobbled Airbus. In fact, prior to launch I was working proposals for a very 787 like (but aluminum body and wing) aircraft for Airbus...
I'm going to be laughing hard if EK buys A350s during round 3. I'll admit I'd cry if the 787 order isn't firmed. I think they are the 787-10 poster child; but I could see an A350/787-10 split. That might set the internet on fire!
Winter is coming.