Several reports from the mailing list have revealed that block device references are not perfectly stable. For example the kernel might oscillate between mmcblk0 and mmcblk1 if it has two memory cards and the detection order is not deterministic.
This epic is about expanding our support to UUIDs to provide stable identifiers instead of direct block device references. The most likely candidate is partition UUIDs, since they are stable even after flashing the filesystem, but may have some problems such as not being supported properly on MBR partition tables. Filesystem UUIDs are also a viable option if combined with client code that makes sure to keep them up to date after flashing a new update.