Is there a way for the materials library to show an image of the proposed material rather than guessing at clicking a Rhino style swatch file ?
The Browse button in the Preferences->Render Libraries opens just the finder. I could check if there is some way to set the finder to get the previews of the files.
However there is one option to get a dialog with the previews. If you go to Windows -> Show Libraries you get the Material Library Dialog of the Rhino. It is still under work and does just display the contents. However we are going to implement drag and drop for the library dialog, so that you can just drag a material from the library dialog to the material editor or the viewport.
The ContextMenu is almost implemented and one should have the option to assign materials from the library to objects.