I think more likely they would use the same PPI as the current iPhone (or the 4/4s for that matter)
The dev's are already accounting for two resolutions for their phone Apps.
3:2 for the previous iPhones
71:40 for the iPhone 5
I could see this going two ways.
4.75in at the iPhone 4s (1296x864) same PPI
4.5in at the iPhone 5 aspect (1280x720) same PPI
4.9in at the iPhone 5 aspect (1400x787) same PPI
I think it's fair to say they will keep the same PPI and the same aspect ratio of a previous iPhone. This would keep life easy for the developers as they wouldn't have to change any code, and Apple would use the same screen technology they are already using.
The dev's are already accounting for two resolutions for their phone Apps.
3:2 for the previous iPhones
71:40 for the iPhone 5
I could see this going two ways.
4.75in at the iPhone 4s (1296x864) same PPI
4.5in at the iPhone 5 aspect (1280x720) same PPI
4.9in at the iPhone 5 aspect (1400x787) same PPI
I think it's fair to say they will keep the same PPI and the same aspect ratio of a previous iPhone. This would keep life easy for the developers as they wouldn't have to change any code, and Apple would use the same screen technology they are already using.