I would like to see a followup to the 29th Century 'Time Cops' as scene on Voyager. Temporal adjusters fixing pivotal points in the timeline. They could do a 'Trials and Tribulations' type show every so often and revisit some existing Trek stories of appear anywhere from the far past to the future of what we are familiar with.
Problem is that Trek over mines an area- TNG made the Alpha Quadrant a local neighborhood, DS-9 did it with the Gamma and Voyager with the Delta. Enterprise has to go into the Expanse to introduce new species and conflict and the next Trek will need to go further out to some unexplored region to come up with unique and fresh stories.
We saw a glimpse of the role and life on the Relativity on Voyager and I thought about what other missions that ship would have- having all of past and future history to explore would be interesting.