Installing CentOS on ext4fs
To allow anaconda to manipulate ext4 filesystems, it is enough to start the installer using the "ext4" parameter on the command line:
linux ext4 [*]
[*] Of course, any other additional options can be added to the command line.
Subsequently the ext4 filesystem will be presented by Disk Druid among all other filesystems. Mind that because of GRUB limitations, it is mandatory to use a separate /boot partition formatted as ext2 or ext3 if your root ( / ) partition is ext4.
For kickstart based installations, just use ext4 instead of ext3 as filesystem. No other change is necessary.