I think his Draytek 2850 may be the first victim of the new BT Sin498 rules after reading through it last night, says to the effect that any Modem/Router found on the network which does not carry certification, will be (more or less) blacklisted!
If this were the case, then I think this would be concerning for all TP-Link VDSL2 models, which haven't been through the MCT testing, especially the TD-W9980 firmware which doesn't support vectoring.
BT wouldn't roll-back G.INP on ECI cabinets to accommodate devices that aren't compliant with SIN 498, that doesn't make sense if they are going to start strictly enforcing SIN 498 conformance testing.
I think it's more likely that it's just changes to the Openreach VDSL2 DSLAM firmware or configuration may result in older and not compliant devices no longer working properly. But not necessarily due to them being explicitly detected and cut off. There was a different problem a while ago, with a particular FritzBox model, I think the 7390, which uses an Ikanos chipset. It lost most or all of its upstream bandwidth except for the US0 band, until FritzBox fixed the problem with a firmware update.