I haven't been able to find a clear reason as to why AUFS seems to have lost support from major distros - although the fact that it requires patching VFS in the kernel and isn't "just a module" doesn't help.
Yeah. That part is true. I think you are probably onto the reason there. For RHEL distributions at least all I've seen included are the fuse based unioning filesystems which is sad.
If overlayFS is in-tree, then it's a possibility to be backported by Red Hat. From the discussions on the GitHub issue tracker, there's a definite problem with custom kernels vs RHEL supported w/ contract.
