I haven't read up on BitFrost in several months, so bits of the model may have changed by now, but as best I can recall, BitFrost is very closely tied to the Linux/POSIX process model. A core part of its process isolation model is the execution of each task under its own ephemeral user and group ID, with system-mediated IPC over DBus.
Things like NaCl (hell, browsers in general) would definitely be safer if operating systems had real isolation features. But obviously NaCl itself can't solve that problem. (Note that isolation is a tiny part of Bitfrost, and an idea that is itself older than the hills).
