I don't think this is an IPv6 address literals problem per se, but instead a URL encoding/specification problem. There really is too much historical baggage her

I don't think this is an IPv6 address literals problem per se, but instead a URL encoding/specification problem. There really is too much historical baggage here to unpack. That's why URL routing is delicate, not to mention canonicalization, fragments, queries, caching, security… If someone gives you a link-local address, you have to know which interface they want you to use, either implicitly or otherwise.