Merrick here...

The Henson Co. has nabbed a script called THE HAPPYTIME MURDERS. Brian & Lisa Henson will produce the project with Jason Lust. Brian's looking to direct.

Written by Todd Berger from a story by Dee Austin Robertson and Berger, the story takes place in a world where humans and puppets co-exist, with the puppets viewed as second-class citizens. When the puppet cast of an '80s children's TV show called "The Happytime Gang" begins to get murdered one by one, a disgraced LAPD detective-turned-private eye puppet -- with a drinking problem, no less -- takes on the case.

...says THIS ARTICLE in Hollywood Reporter.

It's hard not to compare HAPPYTIME to WHO FRAMED ROGER RABBIT (based on the synopsis above). But, since that film's sequel looks as if it'll never materialize, perhaps this'll do instead?