Michelle Forbes. Provided she plays a human or perhaps a Vulcan. She was pretty badass as Admiral Cain on BSG, and since she's currently 45 she'd be the perfect age to play a captain. Kirk at 30-something was a bit young, even though he looked a bit older than his real age. Realistically one'd expect a career of at least 15 years in Starfleet before getting a shot at the captain's rank, probably more than that.