Have you seen this?:
... Why hasn't the populist sudsy brew, already an everyman's refreshment, entered the boxed beverage realm?
Because it's simply more difficult to keep carbonated beer pressurized and oxygen free in large, four-liter containers, according to Thomas Hussey, a recently graduated industrial design student from Australia's University of Technology Sydney .... He knew that costly pony kegs were a poor long-term answer in an environmentally conscious world. So he developed Kegless, a workable solution to the boxed beer dilemma.
With a two-pronged focus on cost and environmental impact, Hussey's invention eschews pricier bottles, kegs and cans in favor of a revolutionary collapsible container that maintains the CO2 pressure while barring oxygen. And it's turned heads. Hussey is one of 14 finalists in the student category of the 2010 Australian Design Award and the Australian component of the James Dyson Award who will advance to the global competition.
More technical info here.