It could be said item 2 was designed into the vehicle.
Some sort of SDO has been included and is used on post-football trains at Mile End, Marion, Oaklands and Hove.
I don't know if Bombardier's SDO system allows for the driving
car to be off the front end of the platform, as opposed to requiring the driving car to be in the platform with only the rear of the train hanging off the back end of the platform.
I do know that the Bombardier SDO was so unreliable (apparently it relied on GPS, not trackside beacons) for one particular operator in England that they ended up turning it off and just using Unit De-Select which locks out the whole 3-car or 4-car EMU rather than just the cars hanging off the end of the platform.
It's also one thing to have a capability, but another to have staff with the training and confidence to use it.
What's the headway limit on the network now? surely the network isn't at capacity.
The average spacing of the ten trains an hour in the peak on the Seaford/Tonsley line is already quite close by Adelaide standards. Six minutes sounds like a lot, but that's also the official lateness margin.
The 'resignalling' in 2013 was a complete flop (an incomplete flop actually, it's still not complete yet) with over $110 million spent for no real change to capacity. The choke point is at the Adelaide end rather than further out on the network, in the morning peak it's common for trains to stack up at the signals approaching the station waiting for a route into the platforms.
Also see the previously mentioned point regarding pandering to the 1.17 people in each car at the level crossings along the route.