I think there need to be more of the human child or adult characters again period, I mean what happened to the characters and the humans feeling like a family?
Not to say they don't try but still...
They need more humans on the street. Somehow the Muppet fan in me hates to have to say it. They need more extras to begin with, every episode for the past few seasons looks like it takes place at the end of the world and only 5 humans and a bunch of Muppets survived. It's a freaking baron wasteland there.
We need to get in more adults because, let's face it, Bob, Gordon, Maria, and Luis won't be around forever (but hopefully they got plenty of time left). Plus, the kids grew up and moved away. If said kids or adults are either disabled or not, we still need to fill out the cast a bit more. Someone needs to have some regular kids come on the street somehow. Leela's family should come over for a visit sometime. Maybe have some nephews or nieces stay with her occasionally to meet the giant Yellow Bird.