Indeed, this requires an additional step in the management of "todo". Personally I am in favor of it because it seems to me that the power of Joplin is to keep the notes and the "todo" in the same place. By connecting them thanks to links and backlinks, you get a powerful system.
Currently, there is a little ambiguity in the use. What is called "due:" is in fact a reminder. If we could consider to have the creation date, the due date, the scheduled date (start date) and the reminder function... we would have all that is necessary for a relatively complete "todo" management. Plugins will do the rest.
In terms of UI, adding an entry in the note properties could be a good first step.
