My theory is that the emma-less way is just not easy enough for people to apply right now for an official release. In it's current state (judging by the HADK-Linux instructions) it involves booting the device into recovery mode and telneting into it to copy the blobs to the oem-partition. For that solution to be official they'll have to automate that process which is not trivial because they'll either have to script telneting into the xperia-x or create an custom recovery image which automatically prepares the partition, then reboots again into fastboot-mode so that they can flash the normal recovery again.