I think that the phrase was so widely used in media criticism that you don't really have to know anything about the penultimate season of "Happy Days" to know that it means a program has sunk to the depths of cheap gimmicry to try to stop bleeding viewership; and that it is clear that its days are now numbered.
I'm betting you could find a whole lot of younger folks working in media that know that "jumped the shark" is bad, without knowing where the reference actually came from. I was never a big fan of HD, and had stopped watching years before that episode aired; I learned the phrase from the place that originated it: Jumptheshark.com, which used to contain a full database of such moments, before it, in turn, stopped getting clicks, and ended up absorbed by TV Guide back in 2009.
There was a time, 20 years or so ago, when the phrase itself implied a certain insider knowledge of the way TV worked; when it was an in-club thing to say. Then numerous television anchors started using it colloquially in interviews, and at that point, you might say that the actual phrase kind of, well, you know ...