It is good to see more awareness of the fact that USB devices can be quite arbitrary things. I remember trying (hard) to convince people that a cell phone was a computer years ago. It's basically the same thing: a USB device can certainly house a computer, for some definition of that.
It would seem that page 11's attack would require that the machine is unlocked and just sitting there. If not, how would it install the keylogger? (It'd be at the password screen, and input would go there.) Otherwise, this is simply a shortcut to install a keylogger and capture sudo. (Which again brings us back to "physical access".)
Page 13: Are there really that many distros that just DHCP any interface? Gentoo (at least mine, I suppose? it is configured by the user, but I thought I chose the defaults here?) doesn't?
Page 17: are there boot orders that put USB first? I feel like HDD is almost always first, given the number of times I need to beg for a prompt in BIOSes, but again, maybe just me?
However, if anything, the above does show how much of a minefield this is…
¹then it's really hard to be secure.