I tend to agree with Raymond here. While I also don't like the positional arguments, I don't think the benefit of API churn them is high enough to remove them. Other than this issue, I have not seen any requests for this change.

I have seen problems because there are positional arguments, but only when people are subclassing these classes. Allowing for subclasses was never a good idea, and is actively discouraged in current simplejson documentation. The dumps default/loads object_hook functionality is sufficient and doesn't have the fragile base class problem. This functionality is is fully compatible with all versions of the library that are in use, back to v1.8 in March 2008, including Python 2.6's json library which IIRC is based on v1.9.