I'm waiting for it to come full circle - the day when the browser VM is so advanced it's basically a VMWare shim and each web page is really an OS that boots up, then we can finally throw away all the development crap collectively known as web duct tape and use real tools for software development.
If someone (Google, Mozilla) pushed for it, this could be merged with a browser API / VirtualBox for speed and completeness, and you could download a paused machine with state.
It's not happening now, but it's possible already.