A prequel would be nice. It's only a question of who should the characters be. Jecht, Braska, and Auron would be a story about friendship, while Shuyin and Lenne's would be a story about love.

As for a sequel, they could do away with it, I just don't know how they'll insert a boss in the middle of the eternal calm. Maybe Seymour? He always returns, so he could be a good boss.