There seems to be so much potential in alternative computing technologies. Why is nobody setting out to build one? (with the obvious exception of quantum computing)
Most alternative techniques I've seen try to use some analog technique to solve a difficult problem. The problem is that scaling the size of the problem requires ever less noise and more accuracy of these techniques and we quickly hit a wall in every case. Memcomputing, for example, can't practically encode more integers than we can test using silicon processors. There's no version of the fault tolerant threshold theorem for analog computers to fix this deficiency.
So really, of all the alternative technologies I've read about, it's only DNA based methods that I'd really be interested in seeing more of.