I've got one- every interface has two ipv6 ips, one real, one link local, which requires a lot of little tweaks in a lot of deployments.
Or if you're doing DSR, the default route ordering rules are different.
Or if you're doing DSR, the default route ordering rules are different.
What kind of tweaks have you required in your deployments because of this?
DSR is a special use case, and with each interface having a link-local address means you don't need to provide globally unique addresses, because the source/destination specify their route explicitly, each hop can use their link-local address. DSR would also require modification if it was using an extended version of IPv4...
Why does link local need to be complicated? Router interfaces facing clients should be fe80::1. That way, every client knows it's default route is fe80::1%eth0 (or similar). Works great for multiple addresses from different networks on the same host, too.