Marc Andreessen back in the browser biz?

Marc Andreessen, founder of Netscape, is reportedly backing a startup called RockMelt that is throwing its hat into the increasingly crowded ring of the browser wars. Little is known about RockMelt at this point aside from rumor and innuendo. The idea, supposedly, is to build a new browser from the ground up rather than just re-engineering the existing browser engine model. It sounds like a daunting undertaking which leads me to wonder- why? If RockMelt ends up being the greatest web browser ever built and is victorious in the browser market share war, what exactly does it win?