Let's hope, it doesn't fall off...

Neat! https://en.wikipedia.org/wiki/Boeing_777X#Wing

Is that the plane that is already 7 years late due to certification issues?

Cool, but then you'd be forced to fly on a Boeing.

You're right, it's a proof of concept: "The extensions, each measuring several metres, will replicate a folding wing in the fully extended position during a flight. They will be fitted with comprehensive testing equipment to capture behaviour in flight and evaluate how the longer wingspan impacts aircraft handling."

It begs for a video too!