There's plenty of evidence around what I say. Just have a look at the date stamps on the side of rail in mainlines and see how old they are on some of the busiest and heaviest sections of network and that just may give you a reality check that once its in, its in for decades and decades.
I've quoted several times the example of Western Australia's request to install 107lb/yard rail instead of the Commonwealth's laid down 94lb/yard standard at the time the standard gauge was being built on the basis of the axleload and tonnage WAGR was proposing for its iron ore traffic and grain. The WAGR had undertaken an extensive analysis of speed, axleload and other requirements looking at railways in North America particularly Canada and also the NSWGR which was already using 107lb/yd rail.
Within months of the line opening, broken rails and derailments started and withing 8 years the WAGR went ahead and funded a 108 million resleepering (heavy duty concrete sleepers) and rerailing (60kg/m head hardened rail). It was compared to the original cost of building the line a huge financial whack.
So let's turn to the beautifully, optimized fit-for-purpose Alice Springs to Darwin railway. A very dear friend (sadly departed) who is a hands on highly experienced track maintenance guy was urgently summonsed to Adelaide not all that long after the new line was open to provide his advice on problems that were already appearing on the new line. He was aware what had been done to save "pennies" as he quoted with wider sleeper spacing, reduced formation profile, 50kg/m rail etc but until he actually saw it in the field he was staggered at what he saw with contract workers battling to keep it together.
He then took a field trip south of Alice to sections where he knew Australian National had installed lighter 80lb/yard rail but on full depth concrete sleepers, standard sleeper spaced track with good formation, ballast etc.
Notwithstanding the age of the rail the track was otherwise in good condition and he remarked to me that short of significant re-spacing of sleepers north of Alice, formation widening on various curves and other works there was no way the new line would perform in the way that it should south of Alice. This was especially apparent with the heavier ore traffic moving on the top end of the railway.
He was staggered that the sleepers north of Alice cannot accommodate heavier rail in the future unlike the 1970's AN sleepers south of Alice and worst of all the major new bridges north of Alice are not rated for heavier axle-loads. If you check the reference material regarding the Tarcoola to Darwin Line you'll see almost a constant line of high grade mineral deposits located either side of the corridor virtually along its full distance. Those sites all present potential opportunities over many decades to come.
So yes we may not have the domestic tonnage to Darwin but no one knows what the future brings in changing traffic flows that might have resulted in land-bridging etc in the future. At least because of the foresight of Commonwealth Railways/Australian National we at least are able to rerail the Trans Line in 60kg/m rail as is being done now but sadly we still can't find the extra money to close up the sleeper spacing so that those sleepers can bare higher speeds and take advantage of the better performance 60kg/m rail delivers again proving my point that investments made in the 70's (40 years ago) are still not being refreshed/enhanced and upgraded for a higher standard railway of Australia's best inter-modal corridor.
So again yet another nation building 100 plus year piece of infrastructure compromised and guess what, the starters gun is at the ready to do it all over again with Inland Rail, we are doing it with Murray Basin Project in Victoria, goodness knows how many cracks we've had at upgrading Townsville-Mt Isa and of course look at Brisbane-Sydney-Melbourne-Adelaide. Around $3 billion of upgrades compromised whilst we spent over $7 billion just on the Hume Highway between Sydney-Melbourne!!!
End of rant!!!