One of the biggest issues for users with the Android operating system revolves around software updates, and that may or may not change anytime soon. For Android N, there will be a new seamless update feature introduced to the system software version that will allow for updates to be more, well, seamless. The functionality, which was borrowed from the Chrome OS platform makes it so that the device is partitioned off into two separate sections at the same time, and more notably, updates can happen in the background because of this which should make updates faster as a user could simply power cycle their device and have the update installed in a much shorter period of time.
What's interesting is that although current Nexus devices will be getting the upgrade to Android N, they will apparently not be getting the seamless update feature that is being opened up with the new version of software, and instead, seamless updates will be left for newer devices only. With this being the case it locks out even the Nexus 6P and the Pixel C, which, are the two most powerful Nexus devices at the moment.
While it was not confirmed that current Android devices besides those in the Nexus lineup would be left out of the mix with seamless updates, chances are that the same restrictions will apply to any phones that are currently on the market and available for purchase. If this ends up being the case it may be a bit of a let down for users, but perhaps the silver lining, though, is that the process for getting seamless updates up and running on a current device would be a difficult one and presumably more trouble than it would be worth for the end user, so this is most likely why Google has come to the decision to leave it off existing Nexus devices. This isn't likely to be too much of an upset for users, as there are many more things coming from Android N that most devices shouldn't be locked out of, and for those that really want the seamless update capabilities, a new device is always an option down the road.