There were rumours of display manufacturing problems holding up the "bigger" iPhone 6. So I wouldn't be surprised to see a minor bump up to an actual 3x pixel size in the next revision.
(This would also give them back a minor marketing advantage that they had briefly when they introduced Retina, as I'd guess most mainstream Android's will stick at 1080p)
(This would also give them back a minor marketing advantage that they had briefly when they introduced Retina, as I'd guess most mainstream Android's will stick at 1080p)