Qantas have only had the Australian business class monopoly since Ansett's demise. Before that there were two products and a lot of corporate types were very loyal to Ansett's business class. When they went guts up there was only one premium product available, so that's where they went.
As mentioned earlier I know one normally business class flyer who recently enjoyed flying with Virgin in their current economy class. He was a former Ansett premium customer and has never liked Qantas much, but that has been the only option since 2001 for people who want big seats, unlimited whiskey and FF points. I can't imagine he's the only former Ansett loyalist who'd be happy to try a different premium airline if Virgin can make it look attractive and offer enough lurks and perks to compete with Qantas.
Either way, 'twill be interesting.