permit values_list flat with more than one key
|Reported by:||rm_||Owned by:||nobody|
|Component:||Database layer (models, ORM)||Version:||master|
|Has patch:||no||Needs documentation:||no|
|Needs tests:||no||Patch needs improvement:||no|
As far as i understand the limitation of flat with just one attribute looks arbitrary  likely to prevent one to shoot himself in the foot getting data of different types / or different meaning. But when you have a model with a ForeignKey to itself that is handy. Some popular application like django-mptt use this kind of models.
If the change is sound, I think i can have a try at doing a patch, should one add a force_flat flag or just remove the limitation and update documentation?