Yes, this is a good candidate! (even though at first glance it uses map{}, so is restricted to XQuery 3.0 + Map Facility implementations).
True; here, we may have to use element fragments as drawback.
BTW the goal is not to have one test harness for all implementations, but to be sure that all implementations are able to run FOTS-based test suites ;-)
Thanks for looking at this! Have you got some other driver implementations so far? Christian