My biggest worry is the ease with which one can accidentally wipe out everything and reset it to factory settings every time you boot up. I might be super careful, but all I need is for my four or seven year old to turn it on wrong, and suddenly I fear I'd have a several hour fix-it session.
If it came with a setting that would let me make changes more permanent (e.g., a BIOS setting), I'd want one in a heartbeat.
This.
My wife accidentally wiped my fully configured Crouton Ubuntu install off the drive when I was first playing with my Gen 1 Pixel. I chatted with a few Google Chrome OS devs right after this happened and managed to convince one that some sort of a setting, even if it's super obscure, would be a good idea, but apparently nothing ever came of it.
Crouton has come along way since then and you can back your chroot off to an SD card now, but it's still a pain point for sure.
That 'setting' exists in the form of opening it up, unscrewing a screw to enable flashing, and then flashing the BIOS.
If you'd rather blow away ChromeOS and install Ubuntu, it's just a few commands on the command line to boot from USB and install Ubuntu.