I don't think it would be. They are expensive and what would you gain by stretching it. All you are adding is more weight to an aircraft and decreasing its payload. Just for a few extra inches of space that no one would really use.
The ER range C-17s are a perfect example of that.
Senators Push Panel For 15 More C-17s
Aviation Week's DTI | John M. Doyle | May 13, 2009
This article first appeared in Aerospace Daily & Defense Report.
Nineteen U.S. senators are urging the Senate Appropriations Committee to include money for more C-17 cargo lifters when it considers the emergency wartime supplemental spending bill for fiscal 2009.
The 30-member committee is slated to take up the $85.3 billion measure to pay for the wars in Iraq and Afghanistan and the swine flu outbreak on May 14.
A letter, written by Sens. Barbara Boxer (D-Calif.) and Christopher "Kit" Bond (R-Mo.), calls on Senate appropriators to include enough money to procure an additional 15 C-17s. Defense Secretary Robert Gates has said he wants to halt C-17 acquisitions at 205 aircraft, either in production or currently flying. Gates also included money for an orderly shutdown of the C-17 line in the fiscal 2010 defense budget request.
The C-17 is assembled at a Boeing plant in Long Beach, Calif., in Boxer’s home state. Bond, a member of the appropriations panel, represents another state with a large Boeing presence.
Boeing advocates in Congress, who have managed to stave off previous attempts to halt production, note that plants in 43 states employing 30,000 people have a part in C-17 production.
Last week the House Appropriations Committee included $3.1 billion for eight C-17s and 11 C-130 cargo aircraft in its $94.3 billion version of the supplemental war spending bill.
In their letter, the senators note that there will be greater need for cargo and transport as the military increases operations in Afghanistan, the Army and Marine Corps increase their end strength and the new Germany-based Africa Command increases its activities.