Can you reference the part of the proposal that states this? I'm reading the following points:

> $GOPATH/src/foo will be imported as foo by non-main package $GOPATH/src/mypkg/p.

> $GOPATH/src/mypkg/external/foo will be imported as foo by a non-main package p anywhere, when p is being built as a dependency of command $GOPATH/src/mypkg/c.

It seems to me this is saying that libraries will use external packages only when built as a dependency of a main package. Again, this means library authors are out of luck.