...but Kirby is a cute pink ball that put himself into chronic storage to one day awaken as a big strong Star Warrior. I'm honestly not sure if you can replace the adorable face of Kirby with a serious plot. I must confess, though, the music styles have drastically changed (or at least within Kirby Air Ride), so that could be the sign of something.
However, Kirby has always had that charm. Then again, Super Mario and Legend of Zelda have had their charm way back in the day of the 80s, however, Legend of Zelda has gone quite a bit dark, and Super Mario's overall style hasn't really changed that much. I guess the question here would be if fans would be ready for change. I'm not sure if fans would love for a 20 year old game series to go to the dark side.
My only argument is that Wind Waker and Spirit Tracks were a bit dark in the story's overall tone, yet they were able to pull it off. Kirby, however, despite it's good gameplay mechanics, seems destined to be a game that looks like it's for kids, have the difficulty for kids, yet be aimed more at teens/adults. We have seen Kirby star in a dark game, that being the Subspace Emissary in Super Smash Bros. Brawl, and it turned out alright; but, that's Smash Bros., not his own title.
So, could Kirby have a dark game all to himself? I have to say the jury is out, but the judge is leaning a bit more on the no side.