We would not need a router or firewall. Probably not a wifi either. All stationary devices will be wired in. And mobiles would use 6G or 7G. Where I live (sweden) you can already get 10Gbe. Now imagine the possibilities. For example VR with less then a ms latency to closest datacenter. Where your device is just a thin client. Microsoft are
already planning to build a DC near major cities, hopefully they are up to something cool.
Default IPv6 (for consumers) is block all incoming (except for traffic related to outgoing). Then with user authorization add allow rules as needed.
So basically no difference between IPv4 vs IPv6.
If you default firewall on IPv6 is allow all... buy a better router/firewall.