The upstream package ships with /usr/share/X11/xorg.conf.d/90-libinput.conf so all input devices are automatically assigned to libinput (see for example https://wiki.archlinux.org/index.php/Libinput#Configuration ). However, the ebuild contains the line DOCS=( "README.md" "conf/99-libinput.conf" ) causing the file to be deleted if FEATURES="nodoc" is set. That in return gives you a X server with no inputs if no other driver (evdev) is installed or a fallback to evdev (if installed).
Installing that file would also be really welcomed by gnome team to allow us to rely on it and not forcing people to manually configure xorg.conf to load libinput over evdev/synaptics https://bugs.gentoo.org/show_bug.cgi?id=580474#c14
Well maybe I should open a separate bug report for explicitly requesting the installation of the file (as evdev does) as, even if both bugs are related, maybe you want to handle it in that way... I am not sure :-/
As a side note, I would like to point to this news item that shows that we should likely rely in the newer 0.19 version for this change http://permalink.gmane.org/gmane.comp.freedesktop.xorg.announce/2415
Well, this days I am facing some issues in "real life" that have caused me to decrease my activity... but I expect to be able to handle this myself if needed probably in a week or so :-)
It turns out that the changes needed for Gnome are already implemented in latest version :D
Fixed by commit 48aa099413299a996cfd797b1bd35d727b1be7be Author: Harri Nieminen <moikkis@gmail.com> Date: Sun Jan 29 18:27:24 2017 +0200 x11-drivers/xf86-input-libinput: Always install conf file.
