"Restore Windows Key" Define command as keyboard shortcut
This is how you do with Karabiner and El Captain.  Just put this in your private.xml.  If you change command+space to open Launchpad it works well also.

&lt;?xml version="1.0"?&gt;
&lt;root&gt;
  &lt;item&gt;
    &lt;name&gt;Make command key activate spotlight.&lt;/name&gt;
    &lt;appendix&gt;(Send an escape key event when escape key is pressed alone.)&lt;/appendix&gt;
    &lt;identifier&gt;private.escape_to_control_escape&lt;/identifier&gt;
    &lt;autogen&gt;
      __KeyOverlaidModifier__
      &lt;!-- from --&gt;
      KeyCode::COMMAND_L,
      &lt;!-- to --&gt;
      KeyCode::COMMAND_L,
      &lt;!-- alone --&gt;
      KeyCode::SPACE, ModifierFlag::COMMAND_L
    &lt;/autogen&gt;
  &lt;/item&gt;
&lt;/root&gt;


This is also interesting for Sierra https://github.com/tekezo/Karabiner-Elements/pull/247