At the Android team's event, it was learned that new seamless update feature in Android N, will not be presented on any current Nexus devices.
While seamless updates' usage of dual system partitions has benefits, allowing updates to the OS to be processed in the background, it may be a bit of a technical adaptation to put on current smartphones. Seamless updates on the Nexus 5X or 6P, for instance, will entail re-partitioning ROM, and isn't possible for an end user to complete without utilizing USB to Computer. In my opinion jumping through hoops as instructions are written assuming you know what you are doing.
Mention of seamless updates in the latest N developer preview, have no bearing on current devices getting seamless updates.
It's very possible we will not see seamless updates on any current Android devices by any manufacturer implemented, and unfortunately or fortunately, it will only be seen on new hardware running N or above. More than likely will on new Nexus devices due out in later quarters.
Seamless updates is borrowed from Chrome OS, in which two system partitions live on the device at any one time. While one partition is in use, the other is free to be updated by the system, so an OS update can be downloaded and installed completely in the background, at which point the user reboots the device and the update will feel little slower than, say, a hard reboot.
It is disappointing that current devices won't get it, while the possibility of someone inadvertently bricking a $500+ phone fairly good, it's no wonder why Google wouldn't make it available.
Although it will not be on current devices it is still something to anticipate with an open expectation.
Let me know your thoughts.