In my experience, baggage is fairly well scrutinised at Qantas Domestic, with a dash of common sense thrown in.
One problem is that the 767 interior was designed in the late 70's/early 80's when pax did not bring on as much luggage and the original 737-800 interior was designed around a two class capacity of 150 - not the 168 or more that you seen at our full service airlines.
Another problem is the refusal of most pax travelling on business to put one of their two bags under the seat in front. This is due to the lack of legroom and it also seems to be some sort of 'status' thing - like claiming the most space makes them feel better.
Many times, I've have pulled up male pax with three or more pieces tell me they are carrying them for a female colleague who has already boarded. I have caught a couple out, but what can one realistically do in most cases?
Cabin crew can be pressured to make it work as current procedures have the baggage loading equipment withdrawn when the last pax scans their boarding pass - which can easily be ten minutes before they enter the cabin (let alone attempt to find room for their luggage). This means that the pax luggage, which is fully compliant with (or even less than) the allowance is not able to fit in the cabin and will follow on the next flight (hopefully). Try telling someone going to Adelaide for 4-8 hours that their bag will be 2 hours behind them! Not a position most cabin crew are comfortable with.
The only answer I can think of would be to rip out seats or restrict the allowance to one piece of DOMESTIC size luggage. Can't see either happening, sadly.
Anyone ever observed how few pax are at the carousels and compared it to the number onboard? I know of CSMs who have delays due to cabin baggage track down the number of pax vs. the number of checked bags. The statistics shocked me.
Back up from the pilots would be great, but do they have the time to be exerting such authority in the current work environment? Do they want to be involved in what the punters see as a purely customer service issue? I do not think many pax make the link between baggage allowances and safety.