If they want to keep the template Jobs has established, they need a person who can drive products (both tech/design sides) and say no in a manner that leaves little doubt.
The exciting part is that there are so many _potential_ worthy successors even when Jobs leaves. The same can't be said of many companies with rockstar CEOs.
Steve Jobs's eye for talent is just as keen as his eye for design. It's an absolutely critical skill and has been an essential component of Apple's success. It's also a skill that too often goes unappreciated. Unlike most rockstar CEOs, he doesn't surround himself with people he can dominate and control.
Indeed, the story of Jony Ive reflects this: toiling in relative obscurity before Jobs' return, Steve immediately recognizes his talent and promotes him aggressively.
I'd have to think that letting the design guy worry about design would probably be the better route, rather than clouding with all of the other business decisions and realities in a major way