Agree with you that whether new tyre in front or rear depends on the condition of the old tyres.
To me, if you start with 4 new tyres, and doing the 2 tyre change method, the old tyres can go to the front. Why? Well, if start with 4 new tyres, in a FWD car (most are nowadays) the front will wear out first. By the time the fronts tyre are bald, the rear will still have 70 to 80 percent. Putting them in front is still safe and also putting them in front will wear the old tyres off first. By the time these two tyre gets bald the rears ones will still have about 80 percent balance and the two tyre change can go on.
This is actually safer because at any time will still have 2 tyres with pattern. If you rotate the tyres at the end of tyre life you actually have 4 bald tyres. That is why if do 4 tyre change better change way before it reaches TWI.....