Before proposing please consider:

• the maintenance cost of the feature → probably not much if coverage.py is used
• implementing it externally (like a shell/python script,
  pytest plugin or something else) → it is already implemented in coverage.py so it should not be too difficult to add

Summary

These questions should be answered:

• why is the feature needed? User convenience
• what problem does it solve? User friendly
• how it is better compared to past solutions to the problem? JSON is easier to read than XML and more common