All NSX's have 2 seats, and because they are Mid-rear cars the engine is right behind the driver, and no you can't sacrifice trunk space for more seats, the only way possible to make an NSX with more seats is to completely modify the body of the car (cut it in half, extend the body, and reinforce the whole car) which would be VERY VERY costly and I doubt an extended NSX would look nice. Also because of the added weight it would be much slower because NSX's rely on a low power to weight ratio to perform on its best.