Once you've overcome the current limitations of HTML by adding native code, offline mode, hardware support, local file access, and so on, is it really meaningful to call the result a "web" app? It's more like a native app written to a cross-platform layer (huh, somebody told me those were evil) that you can easily install from a web page.
The names "web" app and "native" are far too coarse grained to be meaningful. The important parts are the details.
Zero install or heavy weight install? Cross platform or single platform? Offline accessible or not? Safe for anyone to use, or not? Deep linkable or not? Etc.
These attributes can be mixed and matched. And will be.
That went over my head. By 'native client,' are you making a reference to the fact that the push to make all of our apps run on a server is a swing of the pendulum back to the 'mainframe' days and that some day people will be expounding the virtues of writing software to run on the client as the 'new thing?' Or is 'native client' a reference to some new browser technology that I'm unaware of (which is possible)?
Low latency audio, hardware access, virtual memory, et al aren't handled at all or well by NaCl. So something on the scale of Photoshop with it's ability to edit 250MB+ images is nigh impossible with NaCl. Something on the scale of Logic Audio or Cubase, impossible.
Also, with a network bottleneck, mutli-GB 3D games will be unpleasant at best.
