I would like to see a fleet set in 25th century. The major arch of the story would be an Admiral on his heavy-battleship organizing the defenses of the federation's borders. Side stories include (but are not limited to); an exploratory vessel (a solo heavy-ship), seeking new life and new civilizations; a small fleet comprised of a Defiant-like destroyer, a Voyager-like advanced scout ship, and two cruisers (red shirt(s) for a two-parter down the road) and their missions would involve escorting or reinforcing; a small diplomatic/aid/disaster relief fleet comprised of a heavy ship (a galaxy class if it were up to me), a medical ship, a frigate, and a scout ship; and highly-advanced ship (maybe two or a Prometheus-like multi-spliting ship with a captain and his two commanders) dealing with internal affairs (starfleet intelligence maybe).
The first episode would be the Admiral addressing all the captains of their missions. Later in a two-parter/season finale the fleet gathers to prevent an invasion or something. The series would end around an assault on another faction that plans to bring an end to the federation (the Dominion, or the Borg, or some new one) and the fleet we follow is met with other Admirals and their fleets for an all out battle. Sprinkle a few guest star/special appearance ship/fleet episodes, space station episodes, and a colony we catch up with time to time and you have a galactic Star Trek series (and a financial nightmare).