Normally I'd agree with you, but some of the breakthroughs in this space over the last 18 month make it clear that it's not an "if," but a "when." They're positioning to be right there when the moment happens.
This reminds me of the carbon nanotube hype, when they we're going to be the best at everything from batteries to bulletproof vests. There are currently 0 CN products on the market, and it is not clear there ever will be.
Betting on an undiscovered technology that isn't proven to exist is far form a sure thing.
I'd definitely take that bet were I a VC. Note that they've raised about the same amount so far as Juicero did...
We're already seeing some of the first commercially available CNT products, though. Take Vantablack[0] as an example. Or for non-commercial applications of CNT tech, see the CNT-reinforced bicycle frame that Floyd Landis used to win the Tour de France in 2006.[1]
When you consider that Bakelite was invented in 1907, but didn't see major manufacture until the 1940s, or that PVC was discovered in the 1870s, but didn't see commercial production until almost the same time, it doesn't seem like CNT are much behind the timeline for plastics. The entire chemical and plastics revolution didn't really take swing until the 1960s.
CNT probably aren't vaporware, and even if they were I don't know if that'd be too damning a story for Quantum Computers. Quantum Computing isn't "undiscovered" or "[not] proven to exist." Plenty of labs have produced physical quantum logic gates, and IBM even makes access to some of their real 5- and 16-qubit machines available online through the cloud.[2]
[0] https://en.wikipedia.org/wiki/Vantablack
[1] https://archive.fo/20120713061226/http://news.cnet.com/Carbo...
And the higher-qubit demos you've heard about have quite low fidelity, meaning they'll need multiple physical qubits to represent each logical qubit.
When a problem scales like 2^(2x), you can easily reach an insurmountable barrier. I'm not saying they will, mind you.
I am very interested to know if that is the case. From my perspective, your claim seems like an intuitively obvious application of TANSTAAFL, but there are experts who actually understand quantum physics who think otherwise. Layman's intuition is not to be trusted. Therefore quantum computing remains tantalizingly more plausible to me than, say, cold fusion.