Does anyone else actually like the fact that linux has so many distros? To me, its one of the things that made me initially attracted towards linux - choice. Tweakability at its extreme, there is bound to be a distro to run on any hardware from a calculator to a mainframe. There are versions to suit the old school coders, ones to please the Apple fanboys and even ones for artists and multimedia production.
If the entire Linux community focused on improving a few major Linux distros, it would attract Joe User, but make the power users unhappy. Besides, Redhat, Ubuntu and OpenSuse are already doing this anyway with their mainstream focused approach.
If Google made an OS, it would be something aimed towards Joe User, not power users. For a preview, try one of their desktop apps like Google Desktop. Its extendable with widgets, but hogs resources and probably allows Google to collect user habit data. And there's no source code, so its improvements and changes have to only come from Google.
My ideal OS would be secure, stable and fast. It doesn't have to pack many features, there software for that.