If we're throwing away the cruft (which I fully support!), lets do things right. That means planning a (light) abstraction layer for a world where you can use the right tool for the job.
I'm actually starting to wonder if an approach like docker/lxc, but with web features ported to native land may not end up making more sense in the long term.
The idea would be to take all the features of the web that aren't document focused and make them available in userland in a linux container. For example, the linux container would have to ask for permission from the host operating system to get GPS access or Contacts API access. It would also support the ability to use URIs to manage the state of any chromeless "window" object.
It may be easier to take the web to sandboxed containers than bring all the operating systems concepts to the browsers. Basically this would be a LXC User Agent.
http://httplocal.com/ is working on local composition of web pipelines. Micro Xen (Bromium) forks a virtual machine with a fresh copy of the host operating system and browser for every URI.
What do you think of iOS8 extensions and Android intents? Or https://sandstorm.io ? The challenge is maintaining security and composition flexibility. Apple only opened up a few APIs.