I've "manually" compiled a kernel for the cubox-i before. I'd like to look at the Armbian build system, and see if I can get a Ubuntu 19.04 with kernel 4.3 out of it... but I won't have time to try before the next weekend.
With the current Ubuntu 18.04 image from you (Armbian) XFCE seems to be working ok, but without video acceleration. I tried installing ubuntu-desktop (with gdm3), to get to a Wayland desktop, but again would not even get to a login prompt, like with Debian (Armbian Buster). I reverted to XFCE doing a "dpkg-reconfigure gdm3" (choosing "lightdm" in the dialogue).
My use-case for the cubox is file, database, video recording, and audio server... with occasional video output, if possible. I currently don't need a desktop there. In fact a Kodi environment would be ideal.