So the only additional place for footy would be on ONE or the other channels HD channels but they probably wouldn't show something on HD against their normal channel.
Don't get confused with HD and digital. GO!99 is a digital channel but Nine still have their HD channel which simulcasts their main channel which they could show still use for live sport i.e. Wimbledon actually being shown live.
Seven may indeed get a lifestyle channel, but would still have the space depending on what they do to show AFL live on a digital channel.
Also the government will let each network have extra digital channels in the near future meaning they could have three each (The commercial stations).