I would be really interested in a series which focused on the Events after Voyager but not Centered around the Voyager Crew.
I'd love to see A federation "Colonization Fleet" Embark on a journey back into the delta quadrant to colonize space there and to set up trade and diplomacy with the Delta Quadrant species such as the Talaxians ( possibly involving Ambassador Neelix
Of course they would of had to discover a worm hole like In DS9 or some way to get out there and back easily.
The plot could develop so that They accidentally peeve off some alien race who the federation accidentally colonized in their space which could lead to a war themed story arc. Also along with perhaps an more un-wanted business expansion of the Ferengi Alliance sparking tensions between world over lucrative opportunities.