This really is crappy news if it turns out to be true. It seems to be quite successful, and growing in popularity with each wave. I thought I remembered some comments coming out of ToyFair/Celebration III that Hasbro was being coy about the future of Unleashed, saying something "big" was coming next year. It sounded like the format may be changing, but that the line wasn't ending. I'll have to see if I can dig those comments up here...but maybe the "Unleashed as we know it" is the key part of the equation, and we're seeing the line continue, but in a different type of direction. I certainly hope this isn't the end, this was one of my favorite collections.
Edit: Ok, I'm not sure if this was the exact quote I was looking for...but this was in the Hasbro Q and A from Celebration III (from GH.com)...question number 10:
Hasbro Q and AQ:"Will Unleashed be continuing in 2006?"
A: "Yes, and no" (Hasbro would not elaborate on this answer)
Hopefully we'll find out more at Comic-Con.