"ruthless tastemaker" either has to be the CEO or be someone with 100% unequivocal support of the CEO even in the face of unpopular decisions, which is such a rare situation that practically speaking, it kinda does have to be the CEO.
I think Tim Cook knows as well as anyone that Apple needs an executive tastemaker and is willing to give that person all the support they need.
I sort of worry that it's hard for someone to be the executive tastemaker unless he is at the top. With operations types running the company, it will be difficult for any of the creative types to be heard. Steve Jobs is irreplaceable - I'm sure that Apple will continue to succeed for a while longer, but it will be quite difficult for them to anticipate the next disruptive shift in the industry...
Who chooses the tastemaker? If that person doesn't have taste then the tastemaker won't either.
Steve did; he hired Jonathan Ive.
More precisely: he did not fire him. Ive was there before Jobs.