Hi Fabian

>Just to be sure : are you using livecd-tools-21.4-2.el7.x86_64 (and
>corresponding python-imgcreate) packages that are on
>http://mirror.centos.org/centos/7/extras/x86_64/Packages/ and so on a
>CentOS 7 node to build your livecd ?

 I use CentOS-7-x86_64-Minimal-1511.iso to install the system on my pc. I have check the version of livecd-creator is 21.4, and release number is 2.el7


>Also, that ks file isn't updated as only LiveGnome/LiveKDE are
>maintained so maybe compare with the other ks files located on
>https://git.centos.org/tree/sig-core!livemedia.git/4c99f5ea4fa3399f533cd2237badea65d45d6765/kickstarts
>(for example that old ks still points to outdated and non existing
>repositories)

 As you say, the centos-7-livecd.cfg is out of date.  I try the centos-7-live-gnome.cfg, the command is:
    livecd-creator -v --config=centos-7-live-gnome.cfg --fslabel=centos-7-live-gnome --cache=/var/cache/live
 but finally the ISO which i build with centos-7-live-gnome.cfg is also the same structure like:
        centos-7-live-gnome.iso
            |+++EFI
                    |+++BOOT
                        |+++fonts
                        |+++BOOTX64.EFI
                        |+++grub.cfg
                        |+++grubx64.cfg
            |+++isolinux
                    |+++boot.cat
                    |+++initrd0.img
                    |+++vmlinuz0
                    ....
            |+++LiveOS
                    |+++osmin.img
                    |+++squashfs.img

I guess the maybe the different of config file for livecd-tools cause the different ISO. 
Would you please provide the Kickstart config file which used to build  CentOS-7-x86_64-Minimal-1511.iso or other version of offical distro iso.


Best Regards
Qiang Wang