Is there some info regarding this scaling you are referring to? I hate scaling...a lot.
This article is what I'm referencing. They didn't notice any blurriness but it's not like they had a lot of time with it.
I'm not. Look at the iPad Air. You'd think performance would lag given that it's barely clocked any higher than the iPhone 5s, but nope. Performance is better, it throttles less due to its size despite pushing vastly more pixels. The 6 has a comparative cakewalk.
The iPad Air does not create an image larger than the display and then downscale it. The above Ars article did say this about the 6+:
some UI animations and transitions seemed to be a little choppier than they are on the iPhone 6 or our iPhone 5Swell need to wait for our full review to see just how the A8 chip handles the resolution change.
I'm less concerned about performance because I think that will improve with OS updates. I'm more concerned about the sharpness of the 6+ display. My tech OCD would keep me constantly looking for blurriness
IMO the 6+ 1920x1080 display is a temporary bridge to a 2208×1242 one when it becomes financially viable for Apple. I wouldn't be surprised to see a higher density display on an iPhone 7+ so it can display everything at 'native' 3x.