Time to short manufacturers of midrange jets, like Embraer.

That seems like a classic example of "Markets can remain irrational longer than you can remain solvent."

Especially since there are security-circumventing mechanisms developing (private flights) that make heavy use of midrange jets.

Not really though. I regularly travel 1000 - 1500 km on US domestic flights for business on Embraers and CRJs. It's way too long a trip to do by car and high speed passenger rail isn't really a thing that exists here in the US.

Agreed. I would thing that regional jets would become more prevalent on more routes if air travel were to decline.