While screenwriters transitioning into directing usually cut their teeth on television and/or films with modest budgets, people with a strong background in visual arts - such as directing music videos and/or television commercials - will sometimes make their feature film directing debut with a big budget film. As has been pointed out, David Fincher got a big franchise film as his feature debut, as did Joseph Kosinski more recently. Kosinski might be a good choice to direct a Trek movie actually. He'd certainly do a good job with the visuals. Whether he'd get the right tone is the bigger question.