S905X2 needs a newer kernel than the S905X and "internal" install is not supported (old kernel scripts will not work on a mainline kernel). There is no plan to support this in the future either. Use an SD card or USB.
I'm not able to see the standard partitions of Android, do you know if is that due to the kernel? I would be happy using the android partition, USB doesn't provide me a snappy experience (I should probably by a better USB pen), but If I could use it just for boot I would be happy.
I understand there won't be a script in the future but I don't mind doing it manually if someone point me in the right direction, I'm able to restore the box if I brick it, through USB Amlogic burning tool.