Well, to me it does, anyway!
Basically, a coursebook with a topical input text, listening passage or just montage of pictures to the left, and a collection of project/task ideas for students to choose from on the right (including an option to design their own follow up task).
Hence, following a content-based passage about earthquakes (which I lifted from Boost! Reading Lvl 4, by the way), I might feature some project/task options like this:
Projects are completed in a separate notebook, along with follow-up language work based on emergent language as a result of (and process during) the actual tasks.
By my estimates of current average coursebook size, you might have room for 40-60 of these topics, which might even allow classes to pick and choose the ones that most appeal to them...
Of course, it would require a pretty detailed teacher's guide to help those teachers unfamiliar with project work and how to harness and work with emergent language... But heck, isn't that what good teacher's guides should be about?
I've made and used 'coursebooks' like this in the past, and it's really quite stunning how they can, well, grow. And just how truly active and involved they encourage students (and teachers!) to be in the overall learning process.
I would love to see more coursebooks like this out on the market.
But perhaps they just make things (and assume things to be) too simple, right?