Stock Android is dead
Most of what we saw at the unveiling will eventually make its way to future (and some current) Android phones, but not really in the way that Google itself envisioned it. The fact is that in reality, Google's vision for Android M doesn't matter. And that is because Android M, in its pure form, will never make it to the most popular devices running on this platform - the Galaxies, Ones, and Gs of the world. And while most of M's key improvements will still eventually come to these phones, this is guaranteed to happen much later than the Q3 2015 timeline that Google has set.
Stock Android is dead
We can tell you the answer right away: one, the Nexus 6. And would you really use a gigantic 6-inch device that doesn't even fit in your pocket? Our polls say that most people would use a phone with a screen of a size between 4.5” and 5.7”, and that's the sweet spot for an overwhelming majority of users. How many such phones with stock Android do you know of? Exactly: zero.
Stock Android needs its ‘iPhone’, and that’s not a Galaxy phone
Looking at the larger picture of the world, there are a few arguments to be made about stock Android. Those with knowledge of the platform will be quick to say that there are some phones that run Android in a near-stock version: the Moto X (2014 edition), the Sony Xperia Z series, and so on, but the problem is that close enough is often too different to count. Key features are missing, and the one that is missing sorely is the speed of operation of Nexus devices.
It's not just lag, though, it's a whole lot more. Devices from leading brands come with an interface that is not a slight change over stock Android: it's a complete overhaul with different icons, different apps, different animations, different style, no app drawer. It's so different that unless you are a techie you'd have a hard time recognizing that it is actually Android that phone is running, and the change has been so profound that some custom ROM makers like Cyanogen are challenging Google itself and trying to make a Google-less Android.
What we're getting to is admitting a simple fact: stock Android, the version that Google spends billions working on and polishing to perfection, the best Android out there, is not available on a great no-compromise phone that most people would want to use at the moment.