The problem with many2many is not so much an implementation issues as
much as a logical one. There is a reason SQL does not implement APIs
for many2many. Django does what it does by considering a only one case
of many2many, i.e. when there is no info associated to the link.
think of buyer - purchase - product
purchase estabilishes a many2many relation between buyer and product
but it also stores information (quantity of the product, price paid,
date of purchase, etc.)
How should the interface handle the general case? Is there even a
Implementing a many2many a la Django without information stored in the
links may force developer to make wrong design choices.