Generally, there are two ways to drive the boards: by serial line or network(NFS maybe plus NBD). If all switching to NFS, I'm sure there will be other problems in daily using.
For the MAC address issue, it will occur both on current master/tester image layout and NFS deployment if uboot can't get board fused MAC address and pass it to kernel.
For the master image generation, I think the best way is to make LMC be able to create a custom master SD card layout, now it only needs to extend to shrink boot and rootfs partition, and make two or more blank partitions(testboot and testrootfs) with label in one command.