Before, the child model views were all hidden: `custom_urls`, as you can see above, captures anything and is placed before the child models urls.  It was done this way so that the views and url names could still be reversed.

`subclass_view` was there to dispatch the urls captured by `custom_urls` to the correct child model view, assuming a GET parameter `ct_id` was there to tell which child model it was.
But in fact, I don't think it was used.  As far as I know, that `ct_id` behaviour is only used in `add_type_view` and `add_view`.  But we access those views through `urls`, the urls from the parent model, so the child models views were probably impossible to access.

In the new behaviour, I normally included all url patterns.  They look like:
*/admin/myapp/parentmodel/childmodel_*
*/admin/myapp/parentmodel/childmodel_add*
*/admin/myapp/parentmodel/childmodel_history*
etc.

Read also line 465.