Here we go again...
Ok, so we will have the ability to run x86 apps in a browser. But then we will need APIs to make it useful. And if we want to have "browser neutral" applications, which GUI will we choose (so that users are not confronted with something entirely different for each app)?
It seems that Sun has already struggled with all these questions in the past, and succeeded somewhat. It has addressed the issues of security, cross platform GUI and provides a host of APIs all in what would appear to be a more elegant solution (processor independent, not just platform independent).
If I were Google I would help Sun with the big area that it has failed: deployment. Java can work well on the client side, but Sun have made a big mess when it comes to browser integration and compatibility. It is not that difficult, Adobe get it right with Flash (how many flash runtimes do you have on your PC?). Sun have even made some good efforts of late (Java kernel) but the response is all too confused. Sun is a company which develops good technology but can't package it properly for the intended audience. Google is a company which gets the packaging aspect just right.
We seem to see this all the time in IT circles: a technology matures to a point where it is just about usable and then someone throws their hands in the air and starts again in an opposite direction only to end up at the same point 5 years later.
Think how XML-RPC was first portrayed as being a much simpler solution compared to the "overly complex" CORBA. After it became SOAP and then web services and we added all the required WS extensions (security, asynchronous transactions, messaging, etc.) I would argue that it is no less complex than CORBA was. And we lost over 5 years in the process.
Sometimes we would be better of fixing existing technologies which are "almost there" rather than blindly starting again...