In my opinion, one of the things that have made Star Trek Online thrive for so long is new mission content.
I think it was about 5 years ago some older missions were retired to help the larger storyline progress. I understand the objective but some excellent content was removed. These missions could be added to a separate tab outside the main story. This would allow newer players to have additional content and allow seasoned players to re-experience past content such as “The Tribble with Klingons” or “Rapier”.