I love a good Muppet fan-casting, but it's funny to see folks debating what makes a "proper" Muppet adaptation, because... like, based on what? Out of the Muppets' entire filmography, they've done direct adaptations of pre-existing media exactly twice, and neither of them resemble the "one human character surrounded by Muppet Show regulars" model that's often proposed for such casting. Half of the prominent puppet roles in The Muppet Christmas Carol are original puppets created specifically for the film, and all of the major dramatic roles in Muppet Treasure Island are humans. In both films, most of the Muppet Show regulars who do show up appear as "themselves", as invented roles not present in the source material, or in minor cameos. Don't get me wrong, "cast this media entirely with Muppet Show regulars" is a fun mental exercise, but you're not Doing It Wrong if you depart from that model. There's no standard model to depart from.
