Currently, the onboard firmware for the RpI family of boards loads a DTB from the FAT partition, modifies it, and passes it on to the kernel. At a minimum, we know that the onboard firmware injects the board's MAC address into the device tree.
The current model does not allow OTA updates to replace the DTB file since there is only 1 copy in the FAT partition and no redundancy. They standard Mender model delivers the DTB as part of the rootFS so it can be updated OTA. Using DTB-overlays should mitigate this missing feature somewhat but there are likely valid use cases that would require some means to update the DTB OTA.
If we do a standard DTB build from Yocto and deploy that through the root filesystem, then we will, at a minimum, be using a randomly generated MAC address. If we can find a way to query the hardware and inject the actual board MAC address into the DTB then we can remove this limitation.