The bank masking on that BT does to allow FTTC & ADSL to coexist is having a really serious penalty on people with long lines from the cabinet.
It's far to say many people would see a gain of at about 20mbit down if the VDSL2 band plan could use the frequencies that ADSL2+ does. Alternatively the cabinet could try both ADSL2+ and VDSL2 and see what is best suited for the line?
Considering the pressure politicans are putting on BT right now to get more of the country up to the 10mbit/sec this seems like a good course.
OR could notify service providers say 6-12 months in advance that ADSL service to lines connected to FTTC cabinets would be seriously disrupted (not terminated perhaps?) if they don't move to FTTC products.
Anyone left on exchange fed ADSL would suddenly be overwhelmed by crosstalk and would have a very serious incentive to move.
Big problems that I can see are regulatory. But I think it would be worth it to get people on long lines from cabinets up from 5meg/sec to 20-30meg, until more ftth or gfast gets deployed. A stopgap measure for sure.