As I understand it, building a fast train to NTL is faaar more expensive than building one to CBR on account of the nasty terrain, bridges required etc. So why wouldn't you do one to Canberra and kill two birds with one stone - plus of course it's in the right direction to extend to MEL one day.
I know, pigs might fly...
As for freight, you could use CBR now and transfer to trucks down the Federal/Hume Highways back of the clock! Again the road is better than to NTL, though it is further, not to mention that I believe the RAAF ban civil movements at NTL overnight anyway.