I'll show you the significance of the nexus 9 using the 4:3 screen aspect ratio and pushing the ecosystem to adopt it. Its the smartest move google has made since they went with a vertical user experience and phone UI on the Nexus 7 instead of landscape. It changed people's behavior and perception. The definition of crazy is doing the same thing over and over expecting a different result. 16:9 Tablets dont have any advantage outside of watching movies. The cons is that they are awkward to hold vertical and stretches everything out in landscape mode. I can tell already that The apps got better in the process because you are not viewing them in 16:9 landscape mode. Maybe thats one of the reason that developers didnt feel the need to create responsive apps for android because the experience wasnt ideal when viewing it in landscape mode.
They are pros and cons when you use a 4:3 screen but the pros far outweighs the cons. The biggest upgrade out the gate are the apps themselves. They look much better in the 4:3 aspect ratio. They dont look as stretched as before. You can compare the twitter app or the movie preview screen on the nexus 10 and Nexus 9. The layout format is better. The 4:3 screen ratio is bad for movies but great for everything else. The Nexus 9 is a big move which won't be understood for a while. we know android is adopting Multi windows of some sort its coming so lets keep that in mind. Lets bring the overview area formerly known as the recent apps area into the equation. Its a multi tasking area where you can access your chrome tabs. You are going to be in the browser most of the time on the device. The 4:3 screen makes the multi window feature that google is working on more useful on a wider screen. 4:3 Nexus is the guide of the ecosystem. This is was a small but major move IMO. Tablets apps on android just got much better with one simple move.