What exactly are you basing that on? What makes him a 'true product visionary' over say, Cue, Schiller or Ive? I think they all contribute to it in different ways. Steve told Walter Isaacson that Ive understood Apple at its core better than anyone.
I don't think Tim Cook needs to be a product visionary. If Steve felt that was necessary he would have groomed someone else to be CEO. I think it would be a mistake to groom someone to be like Steve. There will never be another Steve. Anyway Tim Cook probably isn't going anywhere for a long while so it seems silly for Lashinsky (or anyone else) to speculate on the next CEO.
Yes, they all contribute. But, IMO, visioneering is not about teamwork or group-think. While input from all sources are helpful and sometimes necessary, it takes an imaginary and strong-minded individual with interest and knowledge of different aspects of a product to pull it off.
Most of the time, what makes a vision successful is not so much how amazing the vision is, but rather the passion of the individual behind it and his drive to make it happen.
If you look at the CVs of the executive teams and what each individual has done before and at Apple, Forstall is easily the most qualified if not the only qualified individual.
And I wasn't talking about another Jobs or Cook going anyhow. So I don't know WTF you mentioned all that in response to my post.