There's only one answer for rural broadband, and it's independant of the future of BT Openreach.
Some time during the last century a telephone line went from being a luxury to an essential, and the Post Office (as it then was) was placed under a universal service obligation. Which inevitably made telephone lines slightly more expensive for everyone in towns and cities.
Around now, a broadband service of at least 4Mbps (I'd say 8Mbps) has gone from being a luxury to an essential, and OpenReach needs to be placed under a universal service obligation. And yes, it means that everyone's fixed line rental will have to go up a bit.
Until they are under a USO it is simple economics that they will concentrate on the 90% of the profit that comes most easily (ie folks in towns and cities) and pay lip-service only to providing folks living a long way away from an exchange with anything but the least good service that they can get away with.