This is a https://github.com/Qiskit/qiskit-terra/pull/6565 follow up This particular issue tracks: - [ ] The `GlobalNamespace._data` is horrendous and needs to be split. More [here](https://github.com/Qiskit/qiskit-terra/pull/6565#discussion_r669145097). - [ ] Merge `GlobalNamespace` and `Exporter`. - [ ] Better Namespace validation and renaming, see [here](https://github.com/Qiskit/qiskit-terra/pull/6565#discussion_r714732791) and [here](https://github.com/Qiskit/qiskit-terra/pull/6565#discussion_r714733921).