I love to see that Purism is progressing a lot with their open smartphone. I look forward to have a 100% Linux phone. Hopefully people who care about privacy, customization and owning their phone will get what they deserve.
Is this really what's special about it? IMO what matters is that it runs free software to the greatest extent possible.
I suspect that most people who will be buying it don't care whether it runs Linux or a BSD or even something like Minix, as long is it presents the familiar POSIX-like interface, has good software available (GNOME, Plasma Mobile), and is loyal to the user instead of to a coroporation [== the user has control over it and can hack on it].
There are drivers for Linux which work on virtually any kernel version. In contrast, the blobs that are in Android are binary blobs that happen to work with one specific kernel binary, they are not drivers for Linux.