Finally moved ALARM from the SD card to the eMMC on my Chromebook. It works! Now have 2x the read speed (with 8GB less space…)
I resized the stateful filesystem from 25 GB to under 1GB, resized the partition, moved and resized the Kern/root-C partitions, set flags, then
cp -ax‘d the root filesystem from the SD card.
I had done a backup of the eMMC before doing any of this, and hopefully I can use that to boot ChromeOS if anything goes wrong (as it looks like I have some new bugs to play with on the 4.6/4.7 kernels…)