It's a good idea but that's all it will remain an idea, for these reasons:
1. Civilian pilots do not have the level of training necessary for close formation flying, and even if they were trained to that standard, any Red Arrows pilot would tell you it's inherently dangerous even if you have the skills and reflex's that are required.
2. Any mistake made could cause loss of life on a massive scale, if you consider that the current A380 airbus can accommodate 560 - 650 passengers the consequences of a mistake don't bear thinking about.
3. By 2050 Airbus will probably be producing an aircraft that will hold 1000 - 2000 passengers so this will make this idea redundant anyway.
In short it's a good idea and I can see the value in wanting to save fuel, but in terms of risk management, the risk to the lives of the passengers is just too great. Anyway but 2050 aircraft fuel as we know it will have become a much rarer commodity so the aircraft manufacturers will have had to produce engines that can fly on vapour or come up with a new power source altogether, again negating the need to fly in this manner.
'This idea will never get off the runway' !
Ahhhh! The old jokes are always the best.