I have created 2 Fedora 21 images for the HummingBoard and Cubox-i.
I will create a XFCE based image too, soon.
In order to extend the root filesystem on this image, you need to run:
fdisk /dev/location-of-your-fedora-arm-media << EOF
e2fsck -f /dev/location-of-your-fedora-arm-media3
More information about Fedora on these boards can be found on this github page