since the use of thumbnail viewer on the rhino4 (maybe around 2008-9) i must say it made wonders and now its fully integrated in rhino 5. i would like to recommend that the same should apply to STL files.
i manage about 5000 and more stl files without any quick access to them.. unless i open them with another program or rhino
could you guys figure a solution,? to view files as thumbnails? that would be amazing