In reality, it doesn't seem very easy to install Linux on the 2015 Pixel or any other Chromebook without either remembering to press Ctrl+D on each boot or by going through a significant set of hoops.
It's like installing Mac OSX on a PC, or Linux on a Mac: you can, but not easily and not in a way that is supported by the manufacturer.
You just have to scroll down in the link to see that there are several limitations that you wouldn't have with an OS that is supported natively.
if the SSD weren't only 64GB... I could put Debian and chrome OS on it.
It lets me run ChromeOS most of the time, and then fire up an Ubuntu session when needed.
I'm shopping around for a new laptop to replace it, that will be more linux-hacker friendly (more keyboard keys, touchpad with real buttons, etc.)