If you can set a chromebook to developer mode, it's quite simple to then sign your own images containing either another bootloader or a custom kernel. The only annoyance from my point of view is that vboot images don't seem to support an initrd.
http://vger.kernel.org/~davem/chromebook_pixel_linux.txt
EDIT: The icing on the cake:
"Every time you boot up you'll need to do that Ctrl-L song and dance, since unfortunately you can't make SeaBIOS the default 30-sec timeout selection. Just deal with it."
Yuck.