Almost, I mean you can only use a single version at a given time. An example would be if an imported library and its importer uses the same dependencies but one used an older API.
> It seems like if go were to add a simple file that maps package name to package URL with a decent support for different URL protocols you could build the same recursive dependency graph and depend on multiple versions of the same package and also different packages with the same name.
I think you could easily build something like that on-top of 1.5's vendoring.