Surely the bi-product of any potential mass migration from ADSL2, 2+ to VDSL2, FTTC must result in increased cross-talk within the cabinet to premises copper infrastructure circuits, many forum patrons can testify that this is already the case as their DSLAM's population has increased.
It's such a pity that BT decided not to roll out vectoring beyond a very limited basis to a very few users, a technology that is proven to considerably reduce cross-talk within the copper circuits.
The Irish telecom provider, Eircom, has very successfully deployed vectoring throughout it's exclusive Huawei estate since 2014.
Not sure if the UK ECI DSLAM's directly support vectoring (with suitable HW & SW upgrades as per Huawei cabinets) perhaps this was a factor in BT not proceeding with the vectoring roll out.
Would the scenario have perhaps produced a similar situation to the G.Inp (re-transmission) fiasco on ECI cabinets ?
My more sceptical side is more inclined to believe that BT decided to invest in G.Fast as this was a technology which would produce more chargeable returns whereas the cost of vectoring upgrades was something that could not be as easily recouped by charging the end users.
G.Fast by virtue of it's line length limitations was only ever going to be a viable option and of benefit to a very small percentage of BB customers, the abysmal take-up of the product certainly reflected this very obvious short coming as did the apparent change of direction by BT away from G.Fast roll out towards FTTP.
Very much stating the obvious I know, vectoring would have provided a benefit to virtually all consumers on FTTC, VDSL service wheras G.Fast was never going to achieve any benefits for the vast majority of users.
Without vectoring, which I don't think is ever likely to happen now, I can't see any way that cross-talk will not increase it's impact on all FTTC subscribers as the migration away from ADSL to VDSL increases.