In spirit of the above comments:
What do you live under a rock?
In all seriousness its not a matter of should they, its a matter of when, its a cash cow for rockstar they aren't just going to let it sit there. Rockstar makes high quality games, unlike some franchises that annualize their games (CoD cough cough) they won't bring it out til they have something new and more interesting to offer in that universe. But yes they will bring another out, when its ready :).