Switched to using a cutom adaptor and a custom layout for todo items. This adaptor takes the todo list directly and interacts through its non-private array exposing methods so that's a design issue resolved. It will allow me to bring in per-event dates.
The edit item activity still isn't on top of things (as I've yet to look into passing and returning more complicated objects) but this switches TodoItem to using the native Date object and shows dates properly within the list.
Added: the TODO date can be edited (and persists appropriately, naturally)
Updated readme.