I've always liked the idea of going back to the Lost Era and picking up a series there, plenty of scope for stories, bridging the gap between TUC and TNG and all the massive changes that went on there. There are also a few ships that could be the focus: Excelsior
(the rumoured Sulu series from the 90s), Enterprise
-B (repairing the damage that GEN did to Harriman, by making him a competent CO rather than the baffoon he had to be to make Kirk look better), or the Enterprise
-C (from the time the ship was launched, she is on a countdown to an honourable death, but before that she would have done the name proud).