I'm under the impression that once a game dev compiled for NaCl x86/x86_64 at all, it ran on all of the Chrome binaries on x86/x86_64, i.e. Mac, Windows, Linux, and Chromebook.
There are already a few games on NaCl, like Don't Starve[0] that work on x86/x86_64-based chromebooks. They just don't run on ARM-based chromebooks -- which is one of the incentives for PNaCl.
IIRC, NaCl could only run in Chrome Web Apps precisely because it was platform-dependent. It looks like PNaCl will also allow ActiveX/Flash-style embedding.
There are already a few games on NaCl, like Don't Starve[0] that work on x86/x86_64-based chromebooks. They just don't run on ARM-based chromebooks -- which is one of the incentives for PNaCl.
IIRC, NaCl could only run in Chrome Web Apps precisely because it was platform-dependent. It looks like PNaCl will also allow ActiveX/Flash-style embedding.
[0] http://www.dontstarvegame.com/