It doesn't matter who owns Openreach as long as its run on commercial lines they have to worry about competition rules, have to be careful about cross subsidies, have to make some sort of profit and the cash to put fibre into every home would have to come from somewhere. Now we're slowly edging there with FTTC and now G.Fast. However to do the last 10% will cost more than the other 90%. It will never commercially even come close to breaking even, you goto the market looking to borrow billions more than you make each year and say we want to borrow this money and spend it on something that we wont even be able to cover the cost of it and you'll get laughed out of the door.
The unpalatable options are :-
1) Slowly keep creeping fibre closer to homes(Works for 70% of the population mainly in towns and cities)
2) Massive government subsidies for rural areas.
3) Ofcom to agree increases in openreach charges so that money can be reinvested in rural areas. Two problems its anti competative as it decreases the incentives for other people to compete in those areas and customers would be up in arms if say £5 to £10 a month was added onto combined bills.
4) Tell rural people they will have to pay for roll out of fibre to there communities. I cant see many people in rural communities accepting being told they have to each pay £10,000 to deliver fibre to there homes.