hi,
it seems that things are handled differently in Rhino 6 on Mac (the folder in which python plugins should be saved has changed).
we will have to release a new installer.
but you can fix the problem manually for now.
just move the folder
/Users/~/Library/Application Support/McNeel/Rhinoceros/MacPlugIns/PythonPlugIns/
to
/Users/~/Library/Application Support/McNeel/Rhinoceros/6.0/Plug-ins/PythonPlugIns/
restart Rhino and everything should be fine.
let me know if this doesn’t work…