A lot could happen in such a fanfiction. For instance, they might have to face an enemy who is specifically targeting married mutants. This would force them to rely on each other even more. Their relationship would be tested, but they would also learn more about each other's strengths and weaknesses. Their love would grow stronger as they overcome these challenges, and they would become an even more powerful couple within the Mutant X universe.
They could travel the world in search of other mutants. Since they are married, they would have a unique dynamic during these travels. Emma could use her powers to sense mutants, and Jess could protect them if they run into any danger. It would be an adventure filled with both danger and discovery.