Yeah, I'm not so sure I believe it. I would like to see the 6 get a 1080P display, and have the 6 Plus stick with the 1080P display as well. The 6 Plus is almost rendering at 2K though. Who knows. My guess is that they stay the same.
I could see that in the redesign of the iPhone 7 but not for the next iteration unless Apple skips the the "S" series this year... camera spec update, and RAM bump would be enough to make most people happy, IMO. I still think we will see the return of a 4" iphone this year too. Can't say why I think this, but I think it will happen.
Why 2K? You can't see the pixels anyway right now so why upgrade? Honestly, there's no use for ultra HD displays on such small displays, unless it's for something like an Oculus Rift. 1080p is fine on 5.5", everything that goes higher requires more power to drive which means less battery life. Making a better looking display, that's where the money's at and Apple knows that.
I don't think it will, but I think it certainly could happen. I'd even say it would be likely for the iP7. Wouldn't require developers to do anything either.
If they boost it to 1242 x 2208, then it will no longer have to downsample everything to the 1080p display. Performance may actually increase, though that sounds slightly counter intuitive. I'm not sure what the effect on battery life would be, but I don't imagine it would be massive; 1080p to 2K isn't a massive jump.
Maybe I'm missing something, but I think it's plausible.
If anything, I think we will see the native 2208x1242 on the plus to solve downscaling issues and less likely an @3x (2000x1125) on the normal one. I think that's the best we can hope for. I always thought that normal retina (@2x) was fine enough, and anything above @3x retina is completely pointless. I've sort of got used to QHD on smartphones, but I originally thought it was really dumb, and I still do. If companies go for FQHD (4K) I really won't know what to say.
I think it could go either way. If force touch requires redesigning a lot of the components from the displays, I could see them increasing the resolution this year. It would be weird to have 750p 4.7" and 1080p 5.5" force touch displays this year only to have 1080p 4.7" and 1440p 5.5" force touch displays for the iPhone 7/7+ and 7s/7s+ for 2016 and 2017. It will be very interesting to find out because the "S" models have always had the exact same displays as the regular models, so this year will be different in one way or the other. Maybe they will call the next iPhone the iPhone 7 and not the iPhone 6s?