I don't see any need for a sapphire display on the phone. The camera lens and the home button where a scratch could lead to failure, yes. But not for the screen itself ..
It's not so much the aesthetic aspect of a scratched display, but the fact is a scratch, even a minor one, compromises the integrity of the display, and makes it much more likely to crack. If Apple can solve the 'brittle' problem of sapphire, or minimize it, by layering sapphire onto Gorilla glass, for example, that could greatly minimize cracked screens on iDevices, and would be a welcome improvement.
Judging by the rumored quantities in the pipeline, it's hard to imagine what else, other than iPhone, iPad etc. screens, this would be destined for.