Indeed. Even copying the 3d models from the installer to the hard drive (SSD) takes several minutes, so I don’t want to install the libraries at all with nightly builds. I have nothing against self-contained installer for the stable release.
Another annoying thing with the installer is that it blindly overwrites previous version and don’t let you handle them as separate. Especially we who test and play with versions should be able to install side by side, for example “KiCad 5” and “KiCad nightly” so that there would be no need for complex instructions for how to do it manually (which I have written to the FAQ).
These changes shouldn’t be problematic or difficult at all (relatively speaking), they would just need some volunteer to do them.