A complete track changes feature would be welcome indeed.
In the meantime, you can use TQAuditor's quick compare feature (or register for free and use a more complete version). It produces a clear Excel comparison report with all highlighted changes. Since a few updates ago, it supports native CafeTran XLIFFs (as well as Trados and other bilingual file formats).
For native projects, also note there is a 'Version' status for the current segment in the target segment toolbar. It allows for a simple form of segment versioning. When the Version status is selected, CafeTran stores automatically the previous translation of the current segment in the alternative translation list. Alternative translations are marked as “A” in the segments grid and can be accessed after the right-click at the source segment editor.