I kind of think Frank Oz has a point though when he said the Muppets (or "Muppets") have become something like "Kleenex" in that whenever you see film/television style puppets on a screen, many people just automatically regard them as Muppets, whether they're actually Muppet characters or not . . . and in a sense, it's true: I've seen videos on YouTube that have puppets included, and people in the comments refer to them as "Muppets," and I think even TV Tropes has sort of genericised the term a bit as well.
I don't think they're as popular as they were in the 70s or 80s, but then again,t here's other things that have been around for so long, that they kind of fall into that whole "Seinfeld is Unfunny" trope . . . like, look at the Looney Tunes in general.