I suppose in a sense, anytime a songwriter modifies a song to take account of a suggestion by anyone else, or even the way listeners react to a song, that is a kind of collaboration, and good songs can get written joint by hundred of people, and more directly by a bunch of people who play together. But basically, I can't see how the core of a song can be produced by more than maybe two people.

Having a bunch of people trying to put a song together in public might be an interesting experiment, but it could hardly be "a sneak peek into all the inner workings of the songwriting process."

But maybe we're into semantics, and the idea is that arranging a song is a part of writing a song, and obviously more people can come into it when it comes to arranging a song. I'd say it's a separate process. That doesn't mean it's not important, but a song can exist in any number of arrangements, and it's still the same song.