Yes, it is quite a common theme. Many fanfiction writers explore the idea of Bella and Jasper as soul mates because it offers a different dynamic compared to the canon relationships in the Twilight series. It allows for new storylines and character developments.
Definitely. Fanfiction often takes existing characters and creates new relationships for them. The concept of Bella and Jasper as soul mates has a certain allure. It can bring out different aspects of their personalities. Since Jasper has a more complex and somewhat darker past compared to Bella, a soul - mate relationship between them could involve him protecting her in different ways, or her helping him come to terms with his past on a deeper level. Also, it can add a new layer of drama and romance to the Twilight - based fanfiction universe.