I can understand that you don't want to spend much time on it. How about removing it from 3.1? We could re-add it when long-term support becomes more likely.
It seems that my statement has surprised you, so let me explain:
I think we should refrain from making design decisions (such as API decisions) without Bob's explicit consent, unless we assign a new maintainer for the simplejson module (perhaps just for the 3k branch, which perhaps would be a fork from Bob's code).
Antoine suggests that Bob did not comment on the issues at hand, therefore, we should not proceed with the proposed design. Since the 3.1 release is only a few weeks ahead, we have the choice of either shipping with the broken version that is currently in the 3k branch, or drop the module from the 3k branch. I believe our users are better served by not having to waste time with a module that doesn't quite work, or may change.