Boeing's (NYSE:BA) commercial-aircraft business has being enjoying a resurgence, and a big part of the pickup in new orders is based on momentum from a big idea: the new 787 Dreamliner. The new plane's promise of high fuel efficiency and reduced maintenance costs immediately caught the attention of the airlines.

A development on Monday seems to provide further evidence that Boeing's vision for the future of commercial aerospace is on target. Mike Bair, head of the 787 program, revealed that Boeing will build a stretch version of the Dreamliner in addition to the three original configurations it had planned, in response to customer demand.

The stretch 787 may not be such a clear-cut positive, however. At least part of Boeing's decision to build the plane appears connected to locking in near-term orders from a single client. More importantly, the new stretch jet could cannibalize sales of an existing Boeing plane.

Bair noted that "about a dozen" airlines have expressed an interest in the stretch 787. According to the Associated Press, though, he mentioned only one airline by name -- Emirates Airlines. Emirates has long sought a larger 787, but Bair noted that now it's "pretty clear that the interest is more widespread than just Emirates." That may be the case, but Emirates also had made it clear that Airbus' larger version of the A350, the European outfit's challenge to the 787, was closer to meeting the airline's requirements than were the three original versions of the 787.

At first blush, it doesn't seem like such a bad thing that Boeing is trying to accommodate Emirates. The problem, though, is that the stretch plane will compete in the same segment as Boeing's last new jet, the 777. Boeing's decision to build the new 787 could be costly indeed.

Aircraft are incredibly expensive to develop and build. New designs are expected to compete in the marketplace for decades -- the 747, for example, has been around for more than 35 years. When Boeing begins delivering the stretch 787 in 2012 as expected, though, the 777 will have been in service for only 17 years. That's a comparatively short time for Boeing to garner a return on its investment.

Rather than being a clear big plus for Boeing, the company's move to build the stretch 787 should be seen as another tactical move to stymie the efforts of competitor Airbus.

Fool contributor Brian Gorman is a freelance writer in Chicago. He does not own shares of any companies mentioned in this article.