Carbon fiber
Carbon fiber has been used to make automobile body panels, Aerospace equipment, violin bows, bicycle frames, wheels, disc brakes, toilet seats (yes, toilet seats!)...
Why hasn't this material been used to make the keyboard keys and hammer actions? Think about it. From Yamaha's website, it says that pine (or spruce) is the best wood material to make keys with and the hammer actions because it has a good weight to stiffness ratio.
Carbon fiber is even lighter, stiffer and stronger than steel! Imagine what could happen if it was used to make piano parts. Because the material is stiffer, energy loss from striking a key will be significantly reduced meaning a faster action. Because it is also lighter, it will also allow for a faster action. Because it is harder than wood, durability of the keys will be significantly improved.
The possible down sides to using carbon fiber for the keys and hammer actions would be the cost of making it - at least initially. Because of the costs, it would be too expensive to produce for only a handful of buyers. Another downside is the limited range of possible parts it can be made.
Carbon fibers' properties also include absorbing vibrations which mean that the lid probably wouldn't be the best made out of carbon fiber since it directs the sound waves. But the opening hatch for the sheet stand, the sheet stand, the fallboad, bench, piano legs, and possibly the piano casing, can also be made of the material. Lighter, stiffer, and stronger than steel (and wood)!
Imagine the possiblities of what carbon fiber can do to piano technology!