The problems with g.fast are largely on the analogue side of things but these problems have a HUGE impact on the vectoring resources (DSP side of things) which in turn has a huge impact on die size and power consumption hence the industry interest in analogue engineers.
The bottom line is that all this complexity/cost/power usage is because we're trying to send a signal down a transmission line which it was never designed for. Internal wiring is going to be a nightmare for most people with g.fast IMHO as the vast majority of it will need replacing with cat5 (or equivalent) cabling.
BT want to sweat the last penny out of their last-mile monopoly infrastructure & I'm sure we can all see the logic in that for BT. Remember that companies in the UK have a legal duty to act solely in the interests of shareholders. However for the rest of us then its complete lunacy on wheels
As I keep saying g.fast has its place but widescale deployment is NOT that place.
We'll see what we see I guess...