obviously ISAT is a videogame but i think if you were gonna adapt it into a linear noninteractive story, a musical would be cute... music would be good for playing with repetition and uncannyness, and obviously the extended stageplay metaphor would be fun and meta.
specifically i'm imagining a separate song for each friendquest, and eventually they get mashed into one song that's too busy to linger in the beauty of each part, hitting the most important lines without the transitions and build-up that are necessary to create a moving piece. then you add another layer of siffrin freaking out and berating themself on top. and finally the act 5 version is barely even a song anymore - just lines, out of context, incorrect, with no orchestral backing.
in general i think you could get a loot of mileage out of reprises with the "siffrin hates themself and everything that's happening" motif winding its way in and overpowering the original songs. until it becomes its own song for mal du pays. and then takes on the king's motif for the bigfrin fight!
i just think it would be neat :3