Just to make things a bit more confusing, the current Android 1440p screens are... not really 1440p. They're pentile, which means their effective PPI is MUCH lower (unless you like to run green on green) and they have no native screen resolution.
If I had to pick between a 1080P RGB panel and a 1440P pentile (diamond) I'd always pick the RGB 1080 because it's visually extremely close while being significantly easier to run as far as rendering work (CPU compositing, GPU rendering).
Read this:
"although this is achieved with a PenTile subpixel layout that makes total subpixel density lower than a conventional RGB stripe, so true subpixel density increases around 20% when compared to an RGB stripe 1080p panel. For reference, going from an RGB stripe 1080p panel to a 1440p panel of the same subpixel stripe would have a density increase closer to 80%." -
http://www.anandtech.com/show/8613/the-samsung-galaxy-note-4-review/4
So it's true that you're still getting some resolution increase with the pentile 1440p, but the trade off is that you're doing WAY more rendering work for a very small actual increase in resolution.
OLED's uneven decay rates are the primary reason for these pentile displays, so hopefully we'll be seeing movement in micro-LED soon (same idea but with each subpixel driven by a microscopic traditional LED). In the meantime it's worth noting that if Apple moved to a 1440p RGB LCD panel they'd be getting a MUCH more significant resolution gain vs those OLED panels for the same processing/rendering cost.
