I've just finished to install FreeBSD 12 on a laptop with an Intel HD Graphics 5500,
with a driver provided by the drm-next-kmod port.

It works fine, and under GNOME 3 gives me good performance when I ask the menu.

To proceed, you can do the following tasks:
  1. Remove your /usr/src directory is present, but not currently tracked on SVN
  2. Track in /usr/src the -STABLE development branch (or -CURRENT if you feel adventurous and have read this section of the handbook
  3. Rebuild the sources for the userland ("world") and the kernel (GENERIC kernel is totally fine, you don't need to customize it), the process has two reboots
  4. Reinstall pkg ( pkg-static install -f pkg), then the software ( pkg ugrade)
  5. Install the drm-next-kmod package, and follow the instructions the message give:
    1. add yourself to the video group
    2. add to /etc/rc.conf kld_list="/boot/modules/i915kms.ko"
  6. Reboot
These steps 2-4 are explained in that section of the handbook, the last is explained in the post just above (but not the binary package seems to work fine out of the box).

With the following to /etc/rc.conf, I got directly gdm popping, without any X configuration:

# GNOME 3 desktop environment
Thanks, I didn't realize there was a package now. Just tried it, seems to work. The only thing for me, on a hires yoga2 is that it made console fonts tiny to the point of being unreadable. However, with this article, http://lme.postach.io/post/changing-console-resolution-in-freebsd-10-with-vt-4 I was able to add a line to /boot/loader.conf to fix that. In addition, I can now, unlike the method in my own article, go from X to console and back again.

I did it this way. Installed a snapshot. Checked out source, but didn't rebuild world, just rebuilt kernel with GENERIC-NODEBUG. Using openbox, I added myself to video group, added the kld_list to rc.conf. I didn't even have to add the xf86-video-intel package.
I didn't have to add dbus or hal to rc.conf. (Though I add dbus for other things I use.)
Anyway, thanks for this, that makes it easier.
I've redone my article to reflect this, much better. I also note that the port is in 11.x but the Makefile has a note that it won't work with 11.x and below.