#1 thing: A series that takes place after the conclusion of DS9/Voyager.
I've got my own idea for what the series would be, I'm sure we all do. Basically post-DS9 the Federation has started becoming more military minded and paranoid of other races, and the main group breaks away from the Federation to rebel against this trend and try to bring it back to its idealistic roots.
Also the captain is a Muslim and the doctor is a double-amputee with replicator hands. And there's a bolian, and a genetically engineered girl who decided to work for the Romulans because she was denied employment on Earth and is thus considered a traitor. And a Klingon guy and Romulan woman who are rebels from their own governments and lovers.
Not that I've spent a lot of time thinking about this or anything.