That's a hard problem - I haven't done any "fiddle" but I've spent a lot of time doing Gedankenexperiment and haven't come up with anything I believe is remotely applicable. The genealogy example I gave is simpler but I'm not sure I've seen an editor for that use-case that's optimal either.

Maybe the problem just can't be simplified further? And as an aside, I wasn't trying to disparage Dave Winer's implementation of tree editing at all.