Zahlen

One of the key issues as to who it will be is the timing of the change. Should Tim Cook become incapacitated for any reason in the immediate future, the obvious choice is Jeff Williams.  He’s the right hand man, and has the ability to takeover on short notice.  

Should the event be in the medium term, then it’s most likely Craig Federighi.  He has a long enough runway in front of him to provide stability for the company for a few years, and similarly he’ll have time to add the gravitas that was mentioned by another poster. 

If Tim takes another 5-7 years before he walks way, then it’s more likely one of two people, John Ternus or someone of a similar demographic who’s currently at the VP level or even a Senior Director who’s a superstar within Apple that we on the outside don’t yet know.  One thing for sure with Apple is that they are VERY predictable, and don’t like to rock the boat - there’s just too much at stake now and having a CEO that has the longevity to see major new products through, from conception to realization is an important consideration.  Also given that many of the leaders in tech are younger, Apple will want to also nurture this as well.