The authenticity of Cook’s email has now been confirmed with Apple PR via multiple sources. If you read his email like a lawyer, it doesn’t guarantee that this is a Mac Pro, exactly — it could be iMacs that somehow better satisfy “pro” users.
But then Forbes got a spokesperson to seemingly confirm that this is indeed about a Mac Pro:
Apple corrects to say desktop updates for 2013 applies only to Mac Pro and not iMac.
That’s a long way off. But it’s not dead.