This is terrifying, particularly since I've agonized over these very same trends you mention and seeing a current attending reinforce them point by point makes it harder to dismiss them as neuroticism.
How bad could things really get? There are a finite number of EDs in the United States and so presumably there are also a finite number of physician shifts required to keep them running. Unlike other specialties, you can't just strike out on your own and set up an outpatient shop as an EM doc so if we ever get to the point where the supply of EM docs exceeds the number of available ED shifts, it'd be game over.
There are 2300 PGY1 spots, soon to be 2500, so that implies a workforce size of 60-70,000 EM docs depending on average career length. There are >30,000 midlevels graduating each year, which works out to about 900,000 midlevels at steady state. If 10% of them want to go into EM that's 90,000, if 20% that's 180,000.
Are there even enough EDs in this country to accommodate anywhere from 150,000 to 220,000 "providers" looking for ED jobs without completely destroying the hourly rates? This sounds like an utter catastrophe happening in slow motion.