I suspected that these partitions could contain code from the NSA.
A Honored Contributor accused me of spreading conspiracy and told some of his insider knowledge, but the whole issue still is not clear.
When I renamed the boot folder - to my big surprise MyCloud still did boot, which proves that uImage on the root partition is not required for a working system.
So maybe sda5 or sda6 also contains that data.
sda7 and sda8 look like a config file with embedded script.
Any educated guesses how MyCloud does boot?