I have never tried to set a local-link address as the default gateway, as local-link address are 'local' so can't be routed. After reading the RFC, I was unable to read the same, what I read is that section 8 is about redirects that are being sent by the default gateway in case there is a better router for the destination host on the local subnet. Comparable to the ICMP-redirect for IPv4.
From what I understand, I have not ever seen setting fe80::1 as default gateway (you also should configure your router with that IP in order for it to be reachable), not that this will have some serious issues in hosts with multiple interfaces, like a loptop with wired and wireless. What I do see is that my Linux host resolves the default gateway to the local-link fe80:: address for my router:
default via fe80::7444:1ff:fe84:adc3 dev eth0 proto ra metric 1024 expires 1585sec
While I put the global 2001: address as my default gateway in the config. On my Aruba controller I see the global 2001: in the routing table an neighbor table. I don't see an RFC violation in that latter behavior and it seems even more secure than accepting unprotected redirect packets.
Also my Ubuntu Linux box refuses to take fe80::1 as default gateway:
ubuntu-server:~ [65] % sudo ip -6 route add default via fe80::1
RTNETLINK answers: Invalid argument
This behavior makes perfect sense to me as well....
Can you explain what you are trying to accomplish, and, where this limits you in your deployment?
Herman