All fine and good, nut I can foresee the following problem....
Subscriber is out, gets an incoming call. Router is connected with (say) 6dB SNRM. Internal wiring is in poor state.
1) The internal wiring is connected, the SNR degrades, and the router drops the connection.
2) Caller gets no answer, and hangs up, router meanwhile is starting to reconnect.
3) Internal wiring is disconnected again
4) Router completes reconnection, achieving same speed and same (fragile) SNRM as before.
...All of above may seem harmless enough. But suppose it is repeated ten times inside an hour, ie somebody is keen to call you... that is the threshold for which BT's DLM reacts to slap an extra two ' stability steps', i.e. 6dB increase in target SNRM.
One assault by DLM is bad enough, but if same thing happens just one more time then the subscriber would find himself in DLM's notorious 15dB prison, from which it is very difficult to escape.
Admittedly, the likelihood of a second occurrence would be reduced as the higher target margin would provide some immunity, but it is not inconceivable.