If the new Pixel goes the way most Intel-based chromebooks have, then it should be possible to have a completely generic Linux / non-Crouton device. I believe support for unlocked SeaBIOS is the feature you're looking for.

I read somewhere, however, that without a hardware developer-mode switch, running out of juice can cause the device to revert from developer-mode and wipe your non-chromeos environment. Check the recent Hacker News thread on the new Pixel for more details.