Most of those take a lot more time and money than YC usually offers. There are some opportunities in "New Defense Technology". Something like a low-cost replacement for the Javelin anti-tank missile based on off the shelf phone camera parts ought to be possible. Of course, once that's out there, every insurgent group will have some. "Explainable AI" is really important. "Stablecoin finance" is mostly how to make sure…
> Is it possible to build a cell phone in the US? Definitely possible, this one is mostly US-built: https://puri.sm/products/librem-5-usa/
Note that it's $1,999+ for mostly made/assembled in USA version, vs. $999 for Purism's made in China version.
And China is more capable at scaling, if the product were ever competing on price rather than principle. So still a ways to go to be competitive at manufacturing.