BT already gives all customers a home hub (router) as part of the deal, this is pretty standard in the uk. They upgrade them every couple of years for you, so going to an IPv6-enabled one is not difficult.
A few cents or dollars per NEW module kills timely standard adoption. We're talking about ISPs, so let's use a well-known evolutionary example with WIFI routers available to users even outside the ISP chain:
First, no wifi at all,
then default / empty passwords all neighbors could steal,
then WEP only because WPA wasn't supported,
then no WPA2...
then (or mixed in with the above):
no support for G,
then no support for N
finally, "support" for N on just 130mbps, but not multiples of it. The unwritten word is also SINGLE band (2.4Ghz)
That is what I remember from a ton of different routers I either got from ISPs, owned, gave away or just troubleshooted. The great fragmentation tells you that it won't be an easy problem to solve. I mean, just check your Wifi now and see how many of the ancient no-nos you can still see from neighbors around you who PAID for their routers --I don't even want to know what they have to settle for at the Modem level.
Providing an upgraded router may not be the same as just "going" up to an IPv6-enabled router. Supply chains take forever (5 years) to provide today's optional features.
If you need more proof that a 2 year cycle for upgrades means nothing, just look at how few top of the line smartphones *refreshed yearly* support 5Ghz bands. Even if you paid through the nose to correct that, you still must leave the 2.4 Ghz band open because your pricy game console [refreshed every 5 years] isn't that lucky or your visitors' gadgets are behind. It's not a pretty picture. Give it 10 or 15 more years