Thanks for the guide, that's pretty much how it can be accomplished.
One minor suggestion, though;

For people using Windows, and hence never needing to mount the ext4fs partitions outside the device, I suggest you change the key
G_EXPORTED_PARTITONS="/dev/mmcblk0" to G_EXPORTED_PARTITONS="/dev/mmcblk0p1"

Reason for that is that even as the WinPC is not going to try to mount other than mmcblk0p1 ever, it is still safer not to try to export the other partitions if you are going to mount them inside the device.