I’m not sure I would like this. An almost-16:9 aspect ratio looks weird in portrait orientation, like the many 16:9 Android tablets. And the iPhone is primarily used in portrait.
I don’t think the iPhone’s screen needs to be bigger, but if Apple’s going to make a change, I’d rather they keep the aspect ratio closer to 3:2.
They certainly don’t need to preserve the 320-logical-pixel width to make it easier on developers. If they change the logical screen resolution, we’re all going to need to update our apps and maintain compatibility with two layouts for a long time regardless of whether they preserve the width.