I do not want the Muppets to be in a Knives Out movie. There is already a perfect Muppet mystery movie. It's called The Great Muppet Caper and is one of the greatest film comedies ever made.
The one exception would be if Benoit Blanc never looks the Muppets in the eye but instead looks directly into the eyes of the Muppet performers just below frame. What, you think he's gonna be fooled by some felt a guy is moving his hand in? He is the last of the gentleman sleuths for God's sake.