It seems that Games Workshop has listened to the fans and has been working on a full-length movie with the expected title Astartes II for a long time.
The teaser trailer, as expected, looks very epic, but there is one "but" - none of the scenes shown in it will be in the movie itself. Instead, the teaser contains a compilation of short scenes from the characters' pasts, and, according to the authors, "at the end it has a subtle hint of the final plot of the film."