ducky Oh, I love system architecture and talking about all the possible trade-offs on designs. I love chatting about this stuff.
I do like the idea of splitting the structure from the presentation. A big challenge with interactive fiction is how to group and structure the story into logical parts so it doesn't turn into one big blob trying to do everything. Things like story, act, scene, actor, prop, etc. That structure also would give your compositor something to hang on.
Taken to the extreme, I think you end up with something like Inform where the line between world-building and creating a piece of interactive fiction blur. It's also a fantastic example of literate programming.
A little more down to earth seems to be Twine which is specifically designed for interactive fiction that can be published to the web . It has several story formats which act somewhat like your compositor concept.
I also just saw Monogatari as another web-based tool but that specialises in visual novels. Looks pretty impressive.
Gah! Beware! This topic seems quite the rabbit hole. I only started looking a few hours ago, but now I'm sinking fast!