The comment below is just a personal opinion.
The beauty of The Seal Hunter mechanics lays in the absence of repetitions. Every weapon, every opponent and even every move presented in the game serves its unique purpose and enriches the game in its unique way. So in my opinion when suggesting weapons one should not just try to diversify the game, but to really think about how his or her proposition will influence the gameplay, what new aspects it will bring to the game and how to balance the inclusion of such an option.
In the case of FN FAL proposed, you have not specified the price, neither did you say about the intended difference between the proposed weapon and its implicit substitute (M16). So it is really hard to judge whether your idea will really change anything in the game.