Folding wing aircraft may or may not be the future of high efficiency airliners. But if it's determined to be a good idea, building the wing fold mechanism won't be a particularly high hurdle.
But at the same time, the benefit would not be significant as well. I am sure it can be done, and sooner or later it will even be a reliable system. But for sure it will add weight and complexity (remember the old DC-3 design philosophy by Ed Heinemann...), it will add new failure scenarios, it will add another source for trouble. The question remains, will it ever pay off compared to a simple state of the art winglet design with practically zero maintenance cost? I seriously doubt that it is the most clever way to gain 1-2% in efficiency, that can probably be done much easier elsewhere.
P.S. I just found the following Statement from Boeing:
“We are spending a lot of effort to make sure we have a a simple design,” he said, “to have a simple and very reliable mechanism, like a landing gear door.”
Hopefully not! Check the long list of SB and AD dealing with Landing Gear Door Trouble...