Version control tools all still operate at the level of *line* additions and deletions, and don't accommodate data with structures that don't map neatly to those boundaries.

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I *think* that certain very high-end "asset management" or "configuration management" tools like [Alienbrain](http://www.alienbrain.com/features) have things like Photoshop and 3D Studio Max plugins to do structured conflict resolution within an editor for structured content, but I have never had the opportunity to use one, so I'm not sure if or how they work.

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This is one of the reasons I have always liked [Bazaar](http://bazaar.canonical.com/en/); the pluggable back-end could hypothetically store any kind of content; the pluggable front-end could hypothetically invoke editors (GIMP, Photoshop, whatever) with appropriate plugins for merging and conflict resolution.

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Unfortunately while the hypothetical consequences of Bazaar's mutability are great, the practical consequences are more problematic; years of format-migration bugs and headaches.