Financially, it's not that great of an idea to add new content to this game. It wont attract new buyers as much as a new game with new characters with tv ads and better online.
This game has bad foundation. Building on it is risky in terms of wasted resources, time and money. At this point I believe getting crash (or any other highly demanded character) would cost more money than the return would be. They would be better used as a hook for new customers in a new version.