That's not just inconvenient, it's verging on paranoia. Most people haven't got the time or the processor cycles to spare to run a separate VM. What's wrong with just disabling plugins for all but trusted sites?
There are lots of browser bugs which aren't plugin related at all. Lots of DOM/parser/JS stuff; the most popular bug class at the moment is use-after-free.
That's not just inconvenient, it's verging on paranoia. Most people haven't got the time or the processor cycles to spare to run a separate VM. What's wrong with just disabling plugins for all but trusted sites?