It does not boot from kernel2, it can't do that.
It can only copy Kernel2 to Kernel and boot Kernel.
I have not tested what happens when both Kernel and Kernel2 partitions are trashed.
I have not tested what happens when jffs2 is trashed and you go back to stock.
That's why some more testing is required.
And I'd still want to have nested partitions on these devices to go back to stock easier.