hi!,
After downloading a few Themes and Plugins in the same folder I got a lot confused which ones are the themes and which are the plugins.
If some pro has a better idea I'm good if not, my idea is simple:
_Plugin.zip && _Theme.zip at the end of each type of zip file.
Add ThemeName_Theme.zip
Add PluginName_Plugin.zip
Also WordPress should alert if a theme is uploaded instead of plugin.