I too have wanted something like what @nielsdybdahl is asking about.
I REALLY wish that the build system would simply provide the capability of a local "libraries" directory under the sketch directory.
i.e. if the sketch directory has a "libraries" directory then that libraries directory would be used just like the sketchbook/libraries directory but have the highest priority in the library search order and on the compile -I include path.
That would make a very simple and fairly intuitive way for users to create a bundled project that included all the necessary libraries.
It would allow Arduino project developers to create something as simple as a zip file that could contain EVERYTHING that is needed to build a project.
It would also allow the entire project bundle - including all the needed libraries, to be source controlled as a bundle..
It would also be simple for the project users as all they would have to do is unzip the project and it could be built with the IDE.
I'm guessing something like this is what @nielsdybdahl is looking for.
An implementation like this would not be difficult to add to the Arduino build tools.
In fact, I proposed this years ago, but it went no where.
--- bill