"As far as Debian/Ubuntu (and crouton), that's fine as far as it goes, but then you don't end up with a Chromebook, just a cheap mini-notebook with flaky drivers."

Hmm, I'm not sure about that. I went the Crouton route on my $169 Chromebook, and now I have both ChromeOS and Ubuntu. Plus I can switch between them quickly. And if I understand Crouton, the chroot is actually using the same kernel and drivers as ChromeOS. I haven't had any driver issues. And it's easy to set up encryption for your chroot. I think it's a good solution.