There are several airlines doing stage lengths that are around that distance already in the NG737, quite profitably I might add. The 737NG is a much higher climber than the A320 and cruises as fast as a 757 now.
American is Running ORD-ANC
ALOHA is running Hawaii to Las Vegas (180 min etops requied)
Southwest is now doing transcon flying as well.
The size of the aircraft doesn't really matter. Its about seatmile costs...
If you give the people enough room within their seats and enough Lavs, (E.G. AA's more room through coach program) the actual size of the aircraft does not matter except for the flight crew's paycheck.
Its all about connecting city pairs. If Ryan air is gonna connect two secondary cities, they will be able to avoid airport crushes, huges lines, expensive parking etc. That has been southwest's formula all along. Southwest pulled out of Denver, SFO etc...
You guys aren't studying closely enough. Its all about point to point these days. The more points the better. The crush on the airline infrastructure is at the airports, not up in the air.
Cheers
Wino