Ironically (maybe not ironic, but at least interesting), I think there's a solid chance his return (and possibly even the entire concept for Cobra Kai) was the result of How I Met Your Mother, and Barnie/Neil Patrick Harris' character was convinced that Johnny Lawrence/William Zapka's character was the good guy in the Karate Kid, and they brought Zapka on the show (I think during the last season as a wedding gift for Barney, he then makes him his best man, iirc... been a while)