It just took me about 30 mins to figure it out, so here’s how to install python plugins in KiCad 5.0 on a Mac.

  1. Make sure your build of KiCad has scripting enabled. It looks like fresh downloads have it by default, but it doesn’t hurt to check. Go KiCad → About KiCad → Show Version Info and make sure that all of the KICAD_SCRIPTING_ flags are set to ON.
  2. Find pcbnew’s plugin search path list. Open pcbnew, and open Tools → Scripting Console. Run import pcbnew; print pcbnew.PLUGIN_DIRECTORIES_SEARCH and you’ll see a list of folders which pcbnew will search for plugins
  3. Move your plugin files/folders to one of these locations
  4. In pcbnew, Tools → External Plugins… → Refresh Plugins. Your Tools → External Plugins menu should fill up with plugins.