Fragmentation has been a huge issue with Android since the very beginning, and it's only gotten worse with time. G1 buyers felt cheated when the Motorola Cliq got Android 2.1 Eclair before they did, and buyers of 2009 and 2010's contemporaries felt alienated when Samsung brought the Galaxy S hammer down, complete with an entirely new interface, and when DROID ads started hitting the air; they were seeing an entirely different Android experience. App developers have worked hard to keep up, but have had serious trouble. Even the biggest names and most popular apps have had issues over the years; right now, for example, some variants of the Samsung Galaxy S7, arguably the most popular Android phone ever, have power on par with mid-range desktop computers, but can't run PPSSPP, a Sony PSP emulator. Different forks of Android and manufacturers updating at their own pace has brought the fragmentation issue to a head, and it looks like the entire reasoning for Google essentially swapping the Pixel and Nexus names is to fight that epidemic.
While Nexus was a pretty good previous attempt to homogenize Android, its secret sauce boiled down to timely updates and a pure experience, things that some manufacturers picked up on and others ignored entirely. With that name seemingly now being mostly relegated to Andromeda OS devices, Pixel is stepping up to the plate, and Google is reportedly bringing a little something extra to the table this time around. Just about every bit of evidence points to some extra features in Pixel devices, some great, some a bit divisive, such as the devices being seemingly impossible to root and thus more secure than the average smartphone. Seemingly, these little touches are going to be crystallized in a Pixel-only version of Android 7.1 Nougat. Various bits of code in the Android repositories seem to point to such a thing, and if suspicions that October 4th's event will be about Pixel are true, then it's likely we'll get a definitive yes or no on that issue at that time.
While the entire concept is speculation running wild for now, it's extremely strong speculation. Google has every reason in the book to rejuvenate their attempt at making Android pure, and adding in a secret sauce in the process will draw in buyers. Nexus buyers wanted a pure experience, but Pixel buyers may end up being after not only that, but also features they won't find elsewhere in the Android world. According to Google CEO Sundar Pichai, Google is going to be a bit more hands-on with the hardware and software for the Pixel lineup than they were with Nexus, and are considering adding more features on top of Android. This could simply mean that Android will become more feature rich at a faster pace and encourage OEMs to update faster, but there is every chance in the world that the Pixel lineup will have features that are separate from the core AOSP code, likely closed source for a specified period of time or even indefinitely to avoid manufacturers grabbing the features without updating.
If the Pixel lineup becomes an overnight success, this would not only light a fire under big names like Samsung to get updates out quicker, but would cut out a clear niche for Google's vision of Android, and give consumers a reason to choose it over what all their friends have or what they see ads for on television. Again, this is almost all speculation for now and should be taken with a grain of salt, but if this gambit is a success for Google, it could mean an entirely new era for Android as a platform at its core, and could mean an entirely different Android landscape when and if Google puts a stop to it and incorporates their aggressive new update scheme into AOSP for all to pluck from, especially if Pixel devices continue to receive cutting-edge updates as soon as they come out of the oven.