The only technically interesting thing here is the lousy remote management setup BT seems to be using.

It's not mentioned in the article, but I'm not aware of a DSL provider in North America NOT using TR-69 to remotely manage the routers given to customers. To properly support customers, you simply need to use something that gives you remote admin capabilities.

"e.g. with remote access via a CPE backdoor, the local ethernet port on the CPE can be put into "promiscuous mode" and all ethernet frames on the local network snagged. Allowing, for example, the snooping of traffic to a networked local printer in an office."

I've actually done this, with the permission of the customer, to diagnose a problem inside the customer's home network. It was actually a badly broken printer killing the wifi.

I know it's not always possible, but if you don't trust the ISP in your home network, don't use the ISP's gear. I don't and I work for one.