According to this:
http://www.serverwatch.com/server-news/where-is-red-hat-enterprise-linux-7.html
RHEL7 will use XFS for the default boot/root.
I could certainly have been out of town, for a while, and missed this. But, to the best of my knowledge, Fedora uses ext4 as the default boot/root. Just sounds a bit strange to me, that this is getting dumped into RHEL