[Symbiote]

Yes.

My mum's boring broadband connection, with a free router supplied by the ISP in the UK, has the functionality next to the port forwarding settings for IPv4.

That's typical. Look up IPv6 pinhole to see how ISPs document it.

[mirimir]

OK, so I suspect that it varies greatly among markets.

But I wonder, is it a fair assumption that the router that you get will either 1) not route IPv6 at all, or 2) route IPv6, and by default deny incoming traffic? Problematic would be ones that routed IPv6, and by default accepted incoming traffic.