People may stop buying routers in an only IPv6 world; you'd just need a switch which are less complicated and cheaper.
Well, they basic consumers would want wifi access point, which means beefy cpu and embedded linux. So while the “router” part might be gone, the “firewall” part will be still there, since it is so cheap and provides visible benefits.
And the advanced people would not buy switches as well, as they’d want some sort of dedicated firewall/IDS box.
And that makes sense. The security scope of "my home" makes a lot of sense. I want every computer in my house to print on the printer without extra authentication. And the tiny CPU in smart doormat can probably be overwhelmed even by a tiny DOS attack.