Mark Millar revealed on his website that while he is "NEVER writing a sequel" to his comic, it seems the film's director Timur Bekmambetov "has an idea for a sequel based on these characters and ideas and they're already making plans with the studio."
Surprising news considering the first hasn't even been shot yet. Millar also revealed that there are "four big names in this picture" with those three already released. The fourth is another big male star (to be) announced inside the next week or two.