The DC9/MD80 type wing is not designed for aftermarket winglets. The load carrying structure and basic design preclude any of these models from ever seeing winglets. Raisbeck looked at something like winglets to help DC9's become stage III compliant but resorted to other techniques stating winglets won't work on that design. The Boeing designs (other than the 717 which started as a McDD design) lend themselves nicely to winglets. Look for a 747-200 winglet kit to come out within the next 2 years significantly helping either range or payload (or both). Finally, the 717 design does not lend itself to transcontinental runs. The wing is great for short to medium haul runs but you just can't get high enough (cruise altitude) to achieve the fuel efficiency necessary. Also, the cruise speed for such a long run would start to factor in as opposed to the Mach .8 the 737 NG's achieve. I suppose 3 o 4 717's could be stuffed with fuel tanks and go the whole way but that ultimately would not be the best way to do it. Long live the 737 NG's for transcon (non-widebody) runs!!!