These are straightforward, finite-effort coding projects.
The Py_VISIT() macro in objimpl.h was introduced to make coding of most tp_traverse slots straightforward, uniform, and obviously correct. For example, see cycle_traverse() in itertoolsmodule.c. Most older modules that define tp_traverse copy/paste/edit the tedious callback dance by hand, and several even define their own work-alike macros. These should be rewritten to use the standard Py_VISIT macro.