I am the author of the thread you linked to in your initial post. I have been trying to make some progress on this for some time. Recently my computer state was corrupted after my laptop (15v3) ran out of juice. As a result I had to reinstall PureOS. I was not able to install it on an encrypted partition as per the instructions on the PureOS wiki page. I managed instead to set up a normal installation (unencrypted partition) and the default setup creates a swap partition which my previous installation (factory shipped) did not have.
I now confirm that I can hibernate my laptop using the poweroff button which you can setup in your power settings. However, I am still unable to get the critical battery issue sorted out.