Great episode.
The discussion on what gameplay is reminds me of a commentary piece written by, to say the least, a rather colorful and passionate person who wrote that the word "gameplay" is the
stupidest word in video games. The crux of the commentary being that when you are talking about gameplay, you are just talking about the game. (Eh, that's a poor paraphrase of his points.)
For me, gameplay/a game is simply how it (the product) plays. With music, it is how it sounds. With a drawing, it is how it looks. With a movie, it is how it looks and sounds. With a game (and gameplay), it is how it plays. From there, I think about all the things that make how a game plays (rules, scoring, goals/objectives, mechanics, controls, tools, attributes, statuses, environments, objects, feedback, results, etc.) and conclude that is what gameplay/a game is.
It becomes difficult to separate where the game ends and where graphics, sound, music, and story begin. This is especially so in Just Dance, Rhythm Heaven, and Ghost Trick which mentioned in the podcast. The difficulty may come from the background question of "What makes a game fun?" and how our personal answer might be that the technical game part of video games aren't the reason why we love to play video games.
Ah, I'm getting off track with a different philosophical discussion.
I'll leave off on where I think gameplay ends and other aspects begin by taking the example of Mario's jump sound effect. That there is a sound effect on a successful jump is important feedback to the player, and such feedback is gameplay. However, as far as gameplay is concerned any short and quick sound effect would be adequate in providing feedback. This is where gameplay in this example ends. That the Mario jump sound effect is the reassuring and joyful sound we have come to know, recognize, and love is where sound design and editing begins.
P.S. Going off from the above, I would imagine a pure gameplay representation of Rhythm Heaven would be sets of lights and sequences of tones that serves as cues for the player input. That is a cold and soulless to imagine for a game that is very much the opposite.