I am interested in the newer kernel because many modules that can be built for it are more mature/stable. Zram being one of them.
With a custom kernel, we can pass a different root location (/dev/sda2 for instance...), and then have a fully persistent environment on the Gen2, like we have on the Gen1, allowing all kinds of fun things. (Like permanently getting iSCSI working without having to resort to ugly hacks). Having more mature versions of Video4Linux modules would be useful too, for people that want to use the NAS as a back-end for security camera storage. (The cameras can be cheap wired ones, sitting directly on the MyCloud via USB, and the MyCloud has the necessary modules to work with the cameras)
I am very interested in the full build instructions, as I would LOVE to fully customize this device.