FCPX has a different data structure, compared to FCP7. It’s not about a “new and improved secret way of writing XML.”
There’s no simple solution here. Different data structures just don’t map to one another. There are ways to bring FCP7 material into FCPX, but it’s a matter of how much organization you’re willing to shed, because there’s no way to map one structure to the other, 1:1.