It's mystifying to me that the iPad still runs what is essentially the same GUI that was designed for a 3.5" display. Those huge icons and wide spacing are inexplicable. Lots of room for GUI innovation.
For the next iPad mini, I'd love to see a 400 ppi or higher display similar to that of the 6+. Bump the A8X GPU from four to six cores, add 4GB RAM, and it will eat Android tablets for breakfast.
At 264 ppi, the iPad Air is no longer competitive. It needs over 326 ppi minimum.
Back in the real world, my expectations are that PPI remains unchanged and iPad sales continue to lag.
I'm not concerned at all with the basic GUI of the home screen. That is about as important as the desktop background in OSX. I don't sit and stare at my iPad's home screen all day, I use apps on my iPad. Apps just need to be easy to find and launch and the design of iOS in this regard is pretty timeless. It is efficient and allows sufficient organization customization to provide easy access to all the apps. The stars are of course the Apps, and the job of the launcher GUI is to provide quick and easy acces to them. The GUI's the apps present to you on the different iDevices are the real measure. This is the domain of the developer, and Apple has provided more than sufficient tools on the different devices to developers in this regard. The groundwork Apple has laid down here is really good.
If Xcode, Preview, TextEdit and iCloud Drive were released as Apps for iOS, you'd pretty much be 99% there as far as a "full fledged" OS goes. The curation of the App store is really the limiting factor, as far as "freedom" goes, because you get the "walled garden" that just isn't present on OSX.
Especially with the new features of iOS 8, the list of things you can't do on an iPad (or iPhone for that matter) that you can on a Mac or PC is continously getting smaller, but those items still on the list are still important enough to not allow them to replace their larger cousins for the average consumer. It's why we still have a Mac mini coupled to external storage as the central hub of our household. We're still a long way from being able to use these devices without having a central photo/media/document library somewhere else.
Biggest problem in this regard is permanence. I don't buy iTunes media because it specifically states that you don't own your purchases, you purchase the right to access the media and it can be removed from the store without notice or recourse, and you don't have the right to transfer any of your purchases to anyone else, say another AppleID. So all our music, movies, TV shows, etc are still purchased brick and mortar and then we either create or download digital copies. This same principle applies to software apps as well especially on iOS. An app goes off the App Store in iOS, and it disappears from your previous purchases and that is a right Apple reserves.
This is the main difference between iOS and OSX. OSX has the Mac App Store, but users still have other sources available to them for software, unlike iOS devices (if we exclude jailbreaking), and you also still have the downloaded installer locally if you kept it.
But back to your quote - the main thing is user experience. As long as it is best in class, it doesn't matter what the actual specs are. I honestly don't see what increasing the resolution of the iPads would do for the user experience - Apple would probably up it enough to use the 3x rendering that the 6+ is using as the new standard, but the point count would probably still be 1024x768 making the usable space the same as before, and would it really be that much better an experience than now? I would much rather they made the displays the same resolution, but improved every other aspect of them. 100% accurate color gamut, even better viewing angles, higher power efficiency, bringing the screen even closer to the touch surface, etc. Make them industry leaders in everything except pixel count. Take cues from what they did with the 6+ screen, which is supposed to be exceptionally awesome.