There is not going to be any aircraft up there in the declared TIBA airspace that has not submitted a flight plan so that is one way ATC at either end can look ahead and see what is out there for passing on traffic information purposes if required.
And as stated earlier why not offset some distance and perhaps fly 100 ft below or above the standard level e.g. FL349.
It is not true to say that Qantas do not fly through TIBA airspace. There was TIBA airspace outside Perth some weeks ago and flights continued through it without incident.
By the way I think it is disgraceful that it has come to this.