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 the issuers don't steal the collateral. Maybe the people behind the stablecoin have an explosive collar welded around their neck. If the price drops, it detonates. That might work.
"Applying machine learning to robotics" has potential. Get bin-picking nailed and get acquired by Amazon. Many people have failed at this, but it might be possible now.
"Bring manufacturing back to America". Is it possible to build a cell phone in the US?
"Climate tech" - think automating HVAC and insulation selection, installation, and analysis. Installers suck at this. See previous HVAC article on HN. A phone app where you walk around and through the building with an IR camera is one place to start. Map the duct system. Take manometer readings. Crunch. That's do-able on YC-sized money.