As I see it, one of the big benefits IPv4 provided was logical addresssing in an easy-to-understand and easy-to-aggregate manner, with small layer-2 networks divided by routers. What we've gone to with IPv6 is a gigantic layer-2 network (the flat autoconfiguration space).
I think we got here when "site-local" went away - we've effectively redefined link-local to mean "site-local," while using globally unique addressing.
Personally, I don't relish the idea of millions of hosts participating in spanning-tree, so I'd rather see us move back toward the direction of using layer-3 addresses to break up layer-2 islands.
How about this for a modest proposal for a capability:
Allow autoconfigured generation of IPv6 interface addresses to use this format:
(one byte VLAN ID) (48 bit MAC address)
(24 bit half-mac) (FFFE) (24 bit half-MAC)
This would allow a CPE router to serve as the gateway for up to 64K VLANs, and wouldn't waste a byte in the middle of the address space.
How about it?
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