It would be wasteful for the NBN and TPG rollouts to target the same areas. As the report notes, last time it happened it created large inefficiency. The time before that was the Betamax vs VHS mess.
What NBN and TPG should do is to meet and create a plan which would see each company rolling out to otherwise unserviced areas. A bulk access provision would allow NBN to retail to customers serviced by TPG infrastructure and vice versa. At some stage in the future, companies could make a business decision to duplicate infrastructure if they believed it was commercially viable.
Consumers would benefit because the rollout would go twice as fast. The could still buy their service from the company of their choice, whichever provides the basic infrastructure. Each company would benefit because they wouldn't be wasting money rolling out fiber to sites that had already been locked into their competitor. It should be possible to argue this case to the ACCC.