There's a great piece on the web by Joe Brancatelli, A Fourth Musketeer in the Skies which investigates the following
"The three airline alliances were supposed to make our lives easier. But how much do they really help business travelers? The solution might just be to get Richard Branson's Virgin carriers and other alliance orphans to band together.
As well as making some very valid criticisms of the existing three alliances, the author says the following,
"A fourth alliance wouldn't be all that hard to build, either. You could start with the three airlines that carry the Virgin name: Virgin Atlantic of Britain, Virgin Australia, and Virgin America...."
He also adds that perhas one of the Gulf airlines might join - Etihad, Qatar or Emirates, which perhaps is less likely....