Daniel Radcliffe and Emma Watson are both two of Hollywood's brightest young stars, but they also have a shared film history through Harry Potter. Both Daniel and Emma became household names thanks to the Harry Potter franchise, although Dan had some prior acting experience. Both landed their roles as Harry Potter and Hermione Granger at a very young age, and both have taken great pains to not be pigeonholed by those roles.
However, their careers have both steadily been taking off since the end of Harry Potter, especially as they're working hard to take on as many diverse roles as possible. Emma has definitely shaken off the goody-goody Hermione Grander image by taking on The Bling Ring and then diversified her resume with Noah, whereas Dan has firmly established his credentials by doing a variety of Broadway plays and dabbling in different genres in film.
Dan has just wrapped the upcoming Frankenstein, and he'll next be seen in The F Word and Horns. Emma just graduated from Brown University and will actually be seen in Regression alongside Ethan Hawke. After Regression, Emma was technically supposed to start Beauty and the Beast, but the project's projected start date might be delayed thanks to Guillermo del Toro dropping out of the project. However, that might free up both Dan and Emma to star together in a movie, especially since both of them have said they're open to considering it in the past.
When Harry Potter initially ended, Rupert Grint, Emma, and Dan all stated that they wanted a break from each other, but with the career trajectories of Dan and Emma getting more and more similar, it's possible that the duo end up in a movie together. They both balance big budget studio films with director-driven indie projects, and they both get drawn to quirky and off-beat roles. It would be a huge fan coup if some studio managed to pull off casting them both in the same movie, but you can bet that Harry Potter fans will turn out in droves.