I think the screen on the iPhone 6 plus is a massive kludge. There is an inconsistency between software and hardware that results in the worst of all worlds: less clear graphics that require more processor time and battery use.
It may be the most fantastic mobile LCD screen ever in terms of figures but the fact that everything is drawn about 15% bigger and then downscaled means that the resulting images are probably less clear on the 401ppi screen than unscaled images on a 326ppi screen.
The problem is compounded by the fact that most apps contain images designed to be pixel perfect for 326ppi screens, so they need to be upscaled by 50% and then downscaled on the 6 plus screen. Hopefully this is done in one operation but I don't know.
As a developer I don't know whether to bother upgrading all my images to what Apple call @3x because they will be downscaled on the one device that would use them. Admittedly a downscaled image would be better than an upscaled one, but not pixel perfect like on every other Apple device. I don't know if it's even possible to get pixel perfect images on a 6 plus!
This all seems to point to pixels becoming irrelevant and coders just relying on the hardware to scale well, which will be fine when the displays are high enough resolution but 401ppi probably isn't enough. At best the end results will look about as good as the old 326ppi retina screens but will use up a lot of power unnecessarily. At worst existing apps will look blurred compared to all other retina iPhones and iPads.
I can only think that the software guys were hoping for a @3x screen but the hardware guys couldn't deliver in time, so we ended up with this kludge. Hopefully the hardware guys will deliver for the 6S plus.
One possible upside is that this reliance on scaling may point to multi-windowing coming soon to iOS for iPads and the bigger iPhones. This would probably use scaling to show two or more apps at once, so maybe the 6 plus is a test run?
If Apple bring out multi-windowing in iOS 8.1 to coincide with the release of the new iPads then I will be pleasantly surprised, but it won't make the screen on the 6 plus any less of a kludge.