3) I think we lost a feature. In traject's own marc4j loader, if you wanted to use your own custom marc4j.jar instead of the bundled one, you could supply a setting with the path to that.

Say a newer marc4j, or a custom marc4j, whatever. We lost that feature, right?  Or you can still do it, but by some way other than the traject setting? If the traject setting is no longer effective, you also need to remove it from doc/settings.md.