DAL tried this. It has not worked. Fact is the new RJ's are more efficient, but with a government that is not willing to address the ATC capacity issues, carbon emissions and the drive to pay for them, plus fuel, it is becoming more and more advantageous for them to use larger jets. The csam goes down, no matter how you tilt the numbers. After all this is just a numbers game.
I do agree that RJ's was the way that it was going, but I think the course has changed.