Recently the Galaxy S4 and HTC One Google Edition have been announced, and there are rumors about an Xperia Z Google Edition, too. It seems obvious that Google is planning here, but right now this program is still at the beginning, and it will depend on all of us to keep this program going.
OEM's seem interested in doing this right now because they believe it would gain them a lot of points with the early adopter and tech savvy crowd, who generally prefers stock Android devices that are managed and upgraded by Google, for at least 18 months, as has been the case with Nexus devices so far.
Ideally, all Android phones would be using stock Android, the version made by Google, just like PC users are using one "stock Windows", the one made by Microsoft. OEM's can add other apps to it, but that's about it. They can't change the whole experience of the operating system, and that's a huge plus for consumers, because one of the main benefits of Windows is that it can be recognized by anyone, and everyone knows how to use a Windows machine, wherever they are.
This is actually exactly the reason why so many are outraged over the forced Metro interface on the PC, because it forces an interface on them that is completely new and it requires a certain learning curve, especially if you're not very tech savvy and can't figure your way around in minutes.
Google has been trying to unify even the custom skin phones, through the Holo framework, so it can be it easier for developers to make more unified apps with fewer bugs, and also make Android more recognizable across devices. But at this point I doubt we'll ever see OEM's turn back from their fully customized interfaces, because now they see that as a way to differentiate between each other's devices, instead of focusing more on hardware, which is supposed to be their expertise, and leave software to Google.
But Google has a plan B now. It wants to slowly introduce more "Nexus-like" devices in the market, and increase the demand for such devices. The OEM's are not going to advertise these devices, so it will be an uphill battle to get these devices, but with any luck the demand for these devices will increase quickly, if the consumers in the Android community vote with their wallets and not just buy them for themselves, but also promote them to all of their friends, instead of other alternatives.
If these Google Edition devices become popular enough, eventually, the OEM's may actually start creating advertising campaigns for them. At that point, Nexus devices should become a large "sub-market" inside the overall Android market, a sub-market that will increasingly increase its percentage of the Android market, to the point where most Android devices would be "Google Edition" devices.
Again, this would standardize many things across the Android ecosystem, and make it easier for consumers to use Android devices, upgrade them with more versions, and almost eliminate the platform fragmentation problem for developers.