Great news, I hope it's true! I agree with the article though, since Tudyk's character died in the movie, why would he be involved? Furthermore, since Book died as well and Serenity herself was essentially destroyed, I'm curious how they would handle a sequel. Lastly, the movie, to me, seemed like a rush to the final chapter of the story. Firefly left so much potential on the table in terms of storylines, character development, unsolved mysteries (i.e. origin of the reavers, Blue Sun, etc) and the movie seemed to capture what should have been the culmination of 4-5 good years of the original TV show. So as I said, the movie seemed to be a showing of what was meant to be - along with how it was all designed to end.
Don't get me wrong, a sequel would be amazing, I'm just curious how they would pull it off. If Whedon had truly planned for a trilogy from the get-go, part of me thinks he wouldn't have done everything he did in the (first?) movie...