I bought a C4 in December and got ALARM running on it pretty quickly with the mainline kernel. The only missing piece is u-boot for which I've posted a PR here: https://github.com/archlinuxarm/PKGBUILDs/pull/1840
As far as I can tell you can use the same device tree for the HC4 and PCIe (for storage) should also work so I encourage you to give that a try.