BT are 'trialling' FTTP, however, but not making much headway
The long and short of it is that once Civil Engineering has anything to do with a telecomms project, you're only looking at an increase in cost and time. Economies of scale only go so far.
The thing is, you see, you've got to run survey the premises, obtain wayleave, clear the roadworks with the council, run the ducts, run the cables, terminate the cables, buy the active kit.
Whilst if you stick to copper delivery to the building, a lot of the headache (especially around wayleave matters) suddenly disappears.
Hence, BT's likely view on the world is Fibre to the Cabinet for the home, and Fibre to the Premises for Businesses (where economical for BT, or where the business would pay the premium).
There is also a high probability that there will be a "postcode-lottery" to some extent on the pricing of BT 21CN access. In regions where BT faces little competition (i.e. out in the sticks), you can probably expect to see a premium fee.
The problem is, for multitude of reasons the UK has been a slow adopter with new technologies. Just look at ADSL. It was first introduced in 1999, and only now, 10-12 years later are we seeing some reasonable quality ADSL products out there at reasonable prices.
I think the honest answer is that we're looking at 10-12 years for 21CN too, perhaps longer if the economy remains depressed. So somehwere around 2017/2018.