the fact that much of BT's copper final mile is life expired and in poor condition
I'm not sure how or what you base that statement on ? Speculation would be my guess. How many on this forum alone, have we seen, where the 'life expired and in poor condition' pair to their house is now providing much higher speed services via FTTC.
Clearly a full FTTP roll out would be glorious, and fairly future proof, but no company has the finances to roll this out, and even if it did, I suspect it's shareholders would be concerned that they would be told to share it's new resource for a fraction of it's install costs, thus making any prospective profits even further away.
The only chance of a fibre to the premises based, full roll out, would be if the Government 'owned' and funded it, then re-couped the costs by charging CP's to provided service to punters over it. This will clearly never happen as it involves both 'common sense' and 'Government' in the same idea.