Going back to what was said earlier... As a disabled person myself, I feel like there isn't a need for another Linda of the show. Linda was great and all when I was growing up, but she was like an extra to most of us that watched that era of the show. The sign language wasn't something most of us held onto, and we just remember her as the deaf girl on SS.
Writing a character into the show with a disability like Autism would be in poor taste IMO. It is like the promotion of a muppet with down syndrome/bipolar/etc. They wouldn't be able to pull it off no matter how hard they try. You can't market a muppet who sees the world in black and white, and the storylines that they would have in the first place would really concern most people. It's like trying to teach a toddler about divorce and how it's not their fault, but there's nothing they can do about it.
As for SS getting cancelled, I think that it'll just BARELY make it to season 50. And it's not going to be about budget cuts, it won't be because Elmo is losing his popularity, and it won't be because of a celebrity. It'll just be the fact that the cast will realize that they're just not into it anymore.
SS is a flagship show for public broadcasting. They wouldn't get rid of it, even if it started to get stale... As it has in recent years. Just like they probably would have still been funding Mister Rogers if he hadn't retired/died. Only in recent years have they cut off the cooking/travel shows that they used to play between the PBS Kids programming, which used to be my naptime unless they were showing Joy of Painting. If they wanted to add to the lineup, they'd most likely axe repeats or shows that are going nowhere. And there are tons of them at the moment.