Re: This is exactly WHY...
BT's links don't work in this way so no it won't impact BT in that way.
This is about CP's using a relatively cheap domestically aimed product instead of using full links back to the headend.
The 'issue' with this is that using consumer grade terminations as backhaul could well impact other users as you could find a whole building connected to one FTTP connection and so the other 32 people connected to the PON don't get what they expect at all.
In reality this is a very strange thing as for OR to actually tell what is going down the pipe they would need a highly intrusive level of inspection which probably breaks a stack of laws irrespective of what people have signed away.
The bigger problem is how do you tell the difference between two cases
a) you run an office building and get an FFTP connection and split it and supply part of the split to your desks and tenants; or
b) you get an FTTP connection and split it to domestic dwellings.
As OR's burble is written case (a) is OK but case (b) is not OK. Go figure.