The legacy application we are migrating into Wagtail does not have a consistent field we can use for Title, so we will generate it based on the value of other fields -- a "name" if it's available. We also need to generate unique IDs for our items, which we will also use for the Slug.
We remove the Title and Slug from the Page form, and set these in code. We set the Slug to a UUID. If we have "name", we'll use that for Title, else we'll use the Slug. If they later set or change the name, we'll update the Title.
It took me some digging to determine how to manipulate these core Django and Wagtail fields, so I've created this example to demonstrate how it can be done fairly easily.
In the formbased Page, we set these in a customer form's
save(); in modelbased Page, we do it in the model's
clean(). Both look pretty similar, so you should be able to adapt
them to your needs.