Ok i have been giving this some serious thought because i am seriously bored with enterprise, and its re-writing of history. But where can star trek go from here? Now think hard about this, dont just say oh they could go with some old character or ship and its future, bare in mind that Nemesis closed alot of doors, Voyager really cant be expanded on and DS9, is also done. A few things to take into account, the war with the Romulans has pretty much ended, the Enterprise is down all its familliar crew, and theres only so many times you can have a battle with the borg before it gets boring:)
The only realistic option is to expand its series by going with a differant race. Maybe a series on the Romulans, with the introduction of the Remans, their war with the Klingons and the new senate. Add to that the introduction of the new warbird, and the Scimitar, i think it allows some good advancement, as it also could cover their history with the Vulcans. But realistically thinking even that would be limited, and perhaps its time star trek called it a day.