Other techniques like changes to the physical construction of the transistor are being worked on. Better transistors still don't address what is likely to be a more immediate problem, that is the wires. Sooner or later you will reach a point where the speed of the wires is more important then the speed of the transistors. Al processes are very close to this point. Using copper for the wires instead of aluminum helps, but only a little.
Life is complex.
It has real and imaginary parts. Yeah, the direction xistors are taking is toward light technology, becuase as silicon structures get smaller quantum effects, like tunneling, are more occurant. I haven't heard anything about it. Seems unlikely to me becuase generating positrons is a very expensive, low-yield process. I don't see it.