"The X-Files" producer Frank Spotnitz has his own production company website for Big Light Productions, and has posted something in his blog about the next movie.
Seems a fan ran into David Duchovny at a benefit on October 2 and asked him what’s the status of the next X-Files movie. Duchovny seemed really positive about it being completed in the next year and out in theatres in two years. Was he correct? Here's what Spotnitz says:
"I’m happy to confirm – as David [Duchovny] has in several interviews – that the rumors about a second X-Files feature film are true. In fact, the studio approached us about doing another feature way back in the summer of 2001, before the ninth and final season of the series was even broadcast.
I can’t speak to the accuracy of the timetable you outline above, but I can tell you that Chris and I have been working on the story for some time. If and when contract negotiations with the studio are finally concluded, we will get to work on the script right away"