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.

Maybe in a decade though.