I don't believe that Jony Ive is being groomed for the CEO role. In my opinion, what Tim Cook is doing is defining his #2. I have believed for some time that your #2 should be your opposite. Jony Ive is a true product guy, an innovator. Tim Cook is an operations guy, a brilliant logistical tactician.
When your #2 is your opposite, it allows you to focus on what you are passionate about, your expertise. Let your #2 focus on the things you don't have passion for. A trusted #2 that is your opposite will make your team more effective because the team gets the best of you.