Trek is rife with one-off characters, locations, etc. that are never seen again after they have fulfilled their purpose. This is intentional on the part of the producers because that is just how episodic storytelling works. But what are some of these dangling plot threads with potential that you have wondered about? I was recently reminded that we never got to find out whether Alicia Travers's life got better after Archer's Enterprise restored the history of 20th century Earth in "Storm Front". To my knowledge, not even any tie-in (non-canon) novels have addressed this point.