You probably would not use an XML parser. All the information needed to send a trackback is the ping-location, that is one ugly regexpression, but only one. I also am no fan of that, rel=trackback is nicer. But the (pragmatic approach to) parsing is simpler than you describe.

I'm actually not okay about the distinction. Trackbacks inform and transport the content, and webmentions inform and are coupled with an unspecified convention to get the content. They end up having the same purpose.