Although i should be paid more than BT's sales guys...
What they should do, is offer new 5 year FTTP contracts. @ £50 per month.
lets say the install cost of FTTP is £1500, at the top end of the scale you mention. £25 a month over 5 years pays for that cost. the other £25 is the data.
Win for the customer, £50 a month is not so bad.
Win for the ISP, they have a customer tied to them for 5 years.
I would sign on the dotted line tomorrow..