Uh, very interesting!
(I was trying to reply your previous post, but it disapeared! But I've found it here again.)
If it works as described, people that asked about X3 connector functionality (in many posts) will achieve an answer.
[edit]I was thinking if it would be possible to use this method to upload a sketch without the bootloader, instead of to burn the bootloader, the same way we do using an external programmer.[/edit]