Here's the thing about the loads and loads of characters: they do not need them any more. Back in the day, 130 hours was a lot to do and the more popular characters were done by people who wouldn't around very often. That's where the likes of Dr. Nobel Price, Chicago the Lion, Betty Lou, etc. come from - they need material and can't use Grover or Ernie when they want.
Now that the long-standing popular characetrs have more availible performers, they can be around more (though E&B are still not around enough). And especially now that the show is shorter and more story-focused, there's no place for random inserts involving people like Colambo or Harvey Kneeslapper.
In little outside projects and videos, I'm fine with seeing Sherlock or Mumford turn up. Maybe a cameo in the background on the show itself.