I honestly don't think it would be very cost efficient for Lockheed to get back into commercial aircraft production. Besides the fact, they'd only be relying on one airframe. McDonnell Douglas tried to improve on the DC10 airframe with the MD-11. Nice airplane, but it didn't exactly live up to it's expectations, performance and range wise. Unfortunately, it's sales didn't meet expectations, either, as Boeing is discontinuing this production line. The name of the game today is ASM's and fuel efficiency, the bottom line. An aircraft with 3 engines just isn't practical, when a similiar aircraft such as the 767-400ER, 777ER, A330-200, can perform the same functions, more economically with 2 engines. The ever growing trend has always leaned towards ETOPS. With the exception, of course, ultra long haul, which is where the 747-400, A340-300/500/600, come into play. Just my thoughts on the subject. Thanks for reading.