The MD roadmap

As far as I know, there are no plans ever to implement this, though Neil is not averse to someone else doing the work. But you don't need it: it took me three hours to come up with an initramfs that could boot my RAID arrays, and after that I didn't care what the kernel's built-in /-mounting code did. (Virtually every distro already has initramfses / initrds that do this.)