Chrome OS releasing at the end of this year is real great news. I have seen a few demos of OS. Though not polished, the OS seemed nice and simple (like all things Google).
But the problem is that, it is geared towards netbooks having SSDs (for speed) and will require net connection in Mbps for it to work properly. I think will have to wait a few years to get a Google OS experience.
And regarding, developing an all together new OS, instead of using Android. Well, I think it's better to have different OS serving the needs of a particular platform.
But, will Chrome OS be able to do what Mac and Linux couldn't all these years? I suspect...