Mobile will kill the NBN
Can already get mobile data for $1/Gig. When that halves again, many if not most houses will simply drop the NBN for mobile. Sure, mobile will never deliver terabytes. But for the average household that just wants a bit of internet TV it should be fine. (More towers means less congestion.)
OTOH, ADSL worked OK for most (but certainly not all) households -- 1.5 megabits is enough for TV once Windows Update is tamed.
That is the design flaw in the NBN. It never made sense.