[Python-ideas] Make types.MappingProxyType hashable

Hello Python-ideas, While answering a question earlier today, I realized that types.MappingProxyType is immutable and unhashable. It seems to me that if all values are hashable (all keys are already guaranteed to be hashable), then the mappingproxy itself should be hashable. Should I go ahead and make a patch for this, or is this a bad idea? Cheers, -Emanuel