I would add this deprecation message to load_plugin when we detect that a plugin is a v6 plugin somewhere around here: https://github.com/opscode/ohai/blob/8a95352b53e3806166da79158b94b90e21f787c2/lib/ohai/loader.rb#L58

Basically we need to say something like:  "<<plugin_name>> is a v6 plugin and v6 plugins will not be supported in the future release of OHAI. Please upgrade your plugin to v7 plugin syntax. For more information visit here: XXX"

Otherwise people will see this message multiple times when they are loading and running v6 plugins...