There is definitely as cost advantage to the regional model, but I'm left wondering how much of an advantage it really is.

For example: SkyWest in 2013 had $59 million in profit on revenue of $3.3 billion. There's a 1.78% return. For this privilege, their mainline partners are willing to pay for all of the associated costs of having a management team and administration teams in place to run this company. So essentially, if you were to remove the senior and middle management and erroneous admin personnel, and push the aircraft over to the mainline certificate, you'd be saving quite a bit of money. You'd lose out on the hourly rate for the crews, but considering it would most likely go very junior, once a pilot had adequate seniority, they'd bid over to an existing airframe... so the years on the payscale past the first few would likely be unused.

There's a definite break-even point, and the margin is pretty close as it is. If the staffing at regionals gets bad enough, we might see someone try to find out exactly how much it costs...