If the R100 is delivered and it looks unlikely that they want BT involved then its by end of 2021
If you read my contribution to your news item regarding Scotland you will see reference to a friend who gets very poor broadband on a dry day and none at all when it's wet or windy
He has been promised faster broadband by the local council, the Scottish Government and the UK government at varying speeds by dates from 2015 extending now, as you say, to 2021 (end)
I am sure you will appreciate his view that it is just all a load of talk, especially when he is told it is better to get 30Mbps rather than a slower fast broadband.
As another contributor opined "I don't care who supplies it, I just need broadband." Many, like my friend, are farmers who are told their claim for EU money can only be made via internet, like his tax return
5Mbps would solve his problems. 2021, with respect, is simply another idle promise that, like all the others before, is simple government ministers reading from a civil servant briefing paper that in 2020 will be kicked, like all the others, into the long grass
If BT will do it for a guaranteed price in the near future let them do it