What sort of structured data are we talking about?
If you format an XML or JSON file with one field per line (or just use YAML) git itself should fit the bill perfectly.
Now, I do see lots of room for a git-like tool targeted at specific existing binary file formats. Microsoft Office and Photoshop files come to mind off the top of my head. (I believe that such tools already exist for those particular formats, but they're expensive and currently have low adoption.)
If you format an XML or JSON file with one field per line (or just use YAML) git itself should fit the bill perfectly.
Now, I do see lots of room for a git-like tool targeted at specific existing binary file formats. Microsoft Office and Photoshop files come to mind off the top of my head. (I believe that such tools already exist for those particular formats, but they're expensive and currently have low adoption.)