Ever heard of the words 'overkill' and 'overcapitalized' ?
Not every device requires less than 40nm let alone less than 28nm let alone 7nm or less.
Do you hire an MBA and pay him $160k pa to run your local fish n' chip shop? ('overkill') Or do you hire someone with good experience and aptitude and pay him $60k pa?
It may be true that there is only so far silicon can go in terms of density and one of the videos says 5nm etc But with Samsung, ST and many others doing a roaring trade at 28nm I think WBT will be just fine for the next 20 years as it is still 1000 x faster than Flash
Two major issues with any material other than silicon:
Availability -new technologies use 'rare earth' materials than although not too rare are nonetheless expensive to mine, refine and hence procure, throwing the cost/benefit equation out so greatly that anything BUT silicon is not feasible for many applications. Think about this in practical terms. Low-cost electronics device manufacturers cannot afford to (and will refuse to) tack on $8-20 more per unit just to have a faster chip if one is not needed for the product.
R&D / re-tooling / learning curve -huge investment is required, decades of R&D etc
"New sorts of transistors can eke out a few more iterations of Moore’s law, but they will get increasingly expensive"
