I quoted those instructions earlier, and they are insanely complicated. There are two issues here: 1st. It is hard to dual boot on any chromebook device, and in part it has to do with the BIOS and ChromeOS security model. The second one is Samsung's fault: some of the kernel bits are binary blobs, so you'll see in these instructions that you need to manually copy a lot of binaries and hope for the best.
This is _not_ an open laptop on my book. I should be able to pop any OS on a USB drive and tell the BIOS to load it, and that does not work. Sure, it can be hacked, anything can be hacked/rooted/cracked. It doesn't mean it's "open".
In fairness to Google, ChromeOS is open source, but the model they follow is not open.