Currently both the Internal and External release date fields require date values (on setup/planning) which are then exposed to all viewers.
The request is to include configuration options that would identify the dates as still tentative.
Thank you for your idea. One suggestion here would be to add a custom workflow status or custom field for releases to let others know that dates are still tentative.
Given the options above and other priorities, we are unlikely to implement this idea at this time. We hope you can understand.