This isn't surprising: Google have been publicly working on a Chrome-powered webview for Android since KitKat came out. It doesn't yet have GPU acceleration or WebGL support but looking at their own public bug tracker the next version of Android should catch up completely. This would mean the normal WebView would be comparable to Chrome for Android in features and performance, like Crosswalk. So a normal PhoneGap Build project would run really well on Android (but only that version and newer, so fragmentation will be a pain, and Crosswalk will remain useful for a long time since it works on 4.0+).
I'd expect they go further and create their own way of publishing "pure" HTML5 apps - like Windows 8 supports, where it's not a web view control in a native app, it really is a whole app made from HTML5 - and possibly also support Chrome Web Store apps, or merge the stores. So then web apps, Chrome Web Store apps, and Android apps all become more or less the same.
This is great news for Android support! The only problem is how long it will take for the next version of Android to get a wide install base - after they actually release it