In certain situations, it makes sense to be able to edit a ManyToMany? relation in both of the datatypes' admin pages. I propose adding an extra keyword argument to ManyToManyField? that makes it appear as though both of the datatypes has the manytomany relation.
Use case:
In my case, I have a bunch of categories and a bunch of items. Items can be in any number of categories and a category can contain any number of items.
If I'm creating a new item and already know that it belongs in categories a, b, and c, I should not have to open each of those categories to add the item to them.
On the other hand, I might be creating a new category and know that items x, y, and z belongs in it, I shouldn't need to open each of x, y, and z to add them to the categories.
With the current limitations, I can only have one of the above.
