How close is the Openreach FTTC network already? As you can FTTC enable cabinets on an exchange without enabling the WBC network expansion at an exchange.
On the smaller exchanges I suspect this will be the preferred method, with the eventual plan to remove the exchange completely, reducing the costs to Openreach.
if you pay for FTTC from Openreach you DO NOT own it, you have simply underwritten the capex costs, and would still need to pay the standard monthly fees, but has the advantage if hardware breaks you are not paying to replace it.
I should point out, just in case its not obvious, 21CN is generally delivered as ADSL2+ from the exchange, FTTC is a step on top of that, and for those only getting 3 to 4 Meg now ADSL2+ makes very little difference. Those who benefit will be those with a 42dB attenuation (3.5km) or shorter line.
If you are on a connection that is faster than 5 Mbps now, and struggling to buffer iPlayer, then something else is wrong. People assume FTTC is needed, but very often the problem may not be the DSL side but the ISP.
Looking at maps.thinkbroadband.com
shows people getting speeds well below what you would expect for the distance from the telephone exchange.
Put it this way, with resonable house wiring, you should have a sync of 5 Meg now right out to a road distance from 3km from the exchange. The people with speedtests posted are all on ISPs who I would NOT recommend for an exchange that is not unbundled, since for these offnet connections, the providers invest very little in the backhaul, which may be the limiting factor. You might find people like BT, Plusnet, Zen, IDNet, Post Office provide better service.