Using a rough hack of $150K for a pilot's yearly salary and $110M for a new A320, eliminating 100 left-seaters from the payroll would pay for itself in just over 7 years. You bet your ass they'd do it for that. Why do you think they're requesting the research from the major airframers and doing some of their own?
100 pilots per airplane?!?
Looking at the fleet-wide numbers:
Delta: 18.08 pilots per airplane ($226)
United: 17.96 ($172)
American: 18.17 ($219)
Southwest: 14.32
Frontier: 16.48 ($142)
JetBlue: 16.20
Spirit: 18.10 ($176)
FedEx: 14.74
UPS: 11.97
Envoy: 14.27
Endeavor: 12.31
SkyWest: 9.93
It's quite an interesting amount of variation, but the one constant is that nobody has anywhere near 100 pilots per plane. Also, you're not eliminating the left-seaters from the payroll, you're eliminating the right seaters. Dollar amounts above are the hourly rate for those right seaters in their 5th year in an A320 for those airlines that fly the 320. It looks to me like even at Delta, eliminating half of the A320 right seaters would save only about $2 million per year per plane, so it's not worth accelerating fleet replacement by much. I would imagine that the purchase price plus additional costs will likely take at least 10 years to pay off anyway.
We used to joke that certain 121 carriers would trade their firstborn for a 1-count drag reduction to save pennies on a flight. It's a joke, of course, but there's some truth to it.
Ryanair's CEO famously proposed replacing right seaters with "highly trained flight attendants". The Pilots' union proposed replacing the CEO with a highly trained flight attendant.
For non-cargo, I can't see the FAA allowing single pilot, due to the unfortunate suicide risk. I would therefore assume they would rather require zero pilots, than one.
There's a lot of reasons why I think it'll go straight from two to zero. The biggest value of the second human in the cockpit is to catch the errors made by the first human in the cockpit.
Another option could be a single pilot, with a non-ATP pilot as second in command to ensure the pilot cant do something stupid, as well as to help with checklists. An ATP pilot + safety pilot with 500 hours is much cheaper than 2 ATP pilots, even if it's not half the cost
Before Colgan 3407, you theoretically only needed a commercial to be in the right seat. Most of the time, in reality, you still needed a lot more than that. 20 years ago, the numbers that would get you hired into a regional right away were 1500 TT with 500 multi.