This would allow for automated analysis on return types that are async/promise. Additionally it would still allow you to use then() the return value and further allow linting to verify your intent of not using await.
For example using promise/prefer-await-to-then and require-await in eslint makes code use 'await' by default which drastically simplifies async code. Being able to meaningfully opt out without a code lint exception would provide clear intent to code reviewers that you're "fire and forgetting"