But you want a more complex challenge? Here you go!
You have a small business office that has two Internet uplinks for redundancy. You want to balance the load across them and failover broken links.
This can be done with literally zero setup with IPv4.
When v6 was “invented” I believe they thought “everyone” would have PI addresses, as was (relatively) common 30 years ago.
If everyone has their own PI space, and used BGP with their ISPs this would also be “zero setup” with v6 as that’s the entire point of BGP and PI addresses.
It was a definite failure of imagination that they did not think of how this would work if you don’t control your own IP space.
If you have ISPs you can peer with over BGP and your own PI IP space this does “just work” as you’d expect. The same way it “just works” with v4 in a NATless world.
A lot of the things that “just work” in v4 are really just NAT sweeping the rough edges under the rug. The same problems exist in v4, but don’t get seen in practice as local / global addresses are effectively always different on your network (unless you’re lucky enough to be a legacy allocation that has an /8 of v4 I suppose).
If you enforce that same “separation” in v6 (with NPT, or NAT) surprise the “problems” also go away, like they do in v4.
The needs for dual-homing and failover were completely glossed over in the IPv6 design, and the IETF has not acknowledged these needs even to this day.
Good times!