...but you will only find the 1 NM stuff in the Orstralian MATS
AFAIK, the ICAO standard is based on the probability model, Oz complies with stuff like the cross-track tables, doesn't with that magic 1 NM. And I agree, all bets are off in the TIBA.
There is the Australian MATS... and then there is ICAO 4444. Agree on TIBA... if they missed, then TIBA worked. There is no Separation Standard.
Whether one is comfortable flying in TIBA is a different question.
A passenger purchases a ticket for a flight and, in doing so, believes that they are paying a premium that ensures that they will arrive at their destination alive and safe, to the maximum extent possible. Unless they are in aviation and understand the reality, they will firmly believe that the flight is being monitored and controlled by an Air Traffic Controller for the duration.
Is it morally correct to board a passenger on a flight that will pass through airspace subject to TIBA and not inform the passenger that their flight will not be subject to an Air Traffic Control service? Is it morally correct to deny that passenger the choice of whether to continue the flight in the knowledge that there will not be an Air Traffic Control service... or not board the aircraft because they personally deem the risk to be unacceptable?