I have been kind of active on F21 testing on my Cubieboards, and have learned a number of unsettling facts. Basically, for the Allwinner SOC, uboot is missing a lot and it probably will not be until spring that key components will work. Most noteably video!
Now I am running Redsleeve successfully on my Cubieboards, and to do that I used the uboot from the Fedora 19 remix which uses the old Allwinner 'special' SunXi 3.4 kernel which has video support, but lacks things like support for the Cubietruck WiFi. See http://linux-sunxi.org/Linux_mainlining_effort for uboot status.
There is a flurry of updates on the uboot list, the target for a major code freeze for upstream is in October, but I don't recognize many Allwinner updates (lots of Freescale posts). But on the Fedora-arm list it was made clear that F21 will be lacking a lot of functionality for Allwinner boards; good enough for servers, but not workstations. And it will be F22 to target what was not included.
I am seriously considering alternative boards like the Wandboard, but it costs more, and my CFO (wife) was really complaining about how much money I recently spent on hardware (even with a 15 month ROI). So for now I am staying with the Cubies.
So on to any possible testing. Karanbir stated in an earlier post to use a F19 build as the basis for a Centos7 build. That would mean the older Sunxi 3.4; which works. But no updates. Not the newer 3.16.
To see what I did for RSEL see:
http://cdn.opensxce.org/redsleeve/el6/cubieboard2/
I have to update the README with some caveats I have learned while working with RSEL (like selinux not working, and you have to install cronie as it is not part of the minimal image).
I am interested in contributing, but... Travel and Holidays over the next month. And most of my Cubies are now in production.