My bet is that Chrome OS will have similar impact to the Chrome browser - encourage everyone to step up their game, but not dominate the market. Google has a lot of money and a lot of bright people, and it acts just like a bright person with little financial concerns: It toys with a lot of ideas, many of them brilliant, but rarely bothers to execute them fully. An OS takes years of frustrating, boring work to mature, I doubt Google has the focus for that.