When AirTran first ordered the 717, AirTran heavily advertised the 717s large overhead bins. With the Southwest/AirTran merger, the 717s are now being considered for elimination, therefore, everyone will have to deal with smaller bins, especially on Southwest's 737 Classics. However, WN has specified their upcoming 738s to have the Boeing Sky Interior, which has even larger bins than the 717.
I was thinking, for a more consistent product, could it be possible that WN will be the launch customer for Heath Tecna Project Amber? While the Project Amber bins are not exactly the same as those from the Boeing Sky Interior, they are a viable alternative, since the Sky Interior cannot be installed on existing aircraft. Project Amber is designed to fit on all 737 Classic, pre-Sky Interior 737NG, and all 757 aircraft.