I prefer relabeling the three points as "Representative", "Iconographic", and "Abstract", and those generally work better for talking about both visual art and gameplay mechanics. Abstract gameplay is easy enough to imagine; Jeff Minter's whole career is based off of it.
Iconographic art at McCloud's extreme is written language (as the purest symbol of an object), with actual icons being slightly closer to both abstraction and representation. Unfortunately I'm not sure what the spaces between text adventures (purely word based) and other iconographic games look like
And then there is "representative", what in games we might call simulationist. But what is the extreme? I would argue it's not a flight sim, but arm wrestling. That is, a game where there is absolutely no abstraction between what you are doing and what your actions represent.
Even so, games need some amount of arbitrariness (scoring, referee) to show its boundaries; a game being a voluntary experience is what makes it a game and not something else. So by necessity there's at least some invisible line between game and reality (aka a magic circle)
This isn't much different from how McCloud's "reality" extreme includes photos, which are notably not reality itself but an artifact depicting reality. No pure thing exists solely as itself, everything is a spectrum, etc
I'm out of the loop on game theorists so i have no idea if connecting the McCloud triangle to game design is an original thought, but it is a useful thought experiment and I imagine could be helpful for designers in the same way that the original can help illustrators.
