A series during the very early days of the Federation has been tossed around by a few people, myself included.It would be difficult to come up with any new series that hasn’t already been done.
Or done to death.
Maybe another prequel dealing with the life of Zephram Cochrane? How he meets Lilly?.
I c as n’t think of anything else
A setting still recovering from the Romulan War would be filled with opportunities for drama and teen angst, being they are constantly trying to attract a younger audience.
Young characters would be picking up the pieces of their fractured lives, while following in the footsteps of their parents, killed or wounded during the war, while rebuilding after the devastation and still trying to reach out into the stars.
It'd be an era of grand expansion and an opportunity to truly examine the roll of Starfleet. Are they a military, or are they explorers?
A this mixed with the political intrigue of the various cultures learning to work together and forming the lasting bonds that made the Federation what we know it became.
Certainly something I'd be interested in watching.