It seems like boot-from-SD is about to become as standard in the x86 world as boot-from-USB currently is. This is generally good news. Also, the need for OS integration is minimal, as it just uses the usual BIOS ABI on doing disk reads.
However, the initrd's shipped by all distributions don't contain the SDHCI driver, and all the installers that I've seen don't support installation on /dev/mmcblk*
I've now filed bugs for all the major distributions about this issue, and you can find more information at this wiki page on installing Linux on a bootable SD card. Let's hope that the distro's consider this feature important enough to add support to it to their next releases to make sure at the time the users buy this kind of hardware they can install the then-existing versions of those distributions.