So much misunderstanding caused by an omission by El Reg. What is missing from the article (as of lunch time Wednesday) is that Openreach will only be expected to pay up to a certain amount. Same as is already the case for voice lines. If the cost goes above that amount the customer has to pay.
So the cost to Openreach depends what is picked as the standard cost. For voice lines this is currently around £4,000. I assume it'll be a bit higher for data lines but there is going to be a cap of some kind. Hard to connect customers are going to have to reach into their own pockets to make up the difference.