I wrote an initial post on the first chapter of Storythinking, which will probably drop tomorrow morning. I invited Tracy to comment within the post, before it is published. This led to a bit of confusion over how to actually make this happen. I had already made Tracy a co-author of the post, but it turned out this didn't mean she could even see it. I sent her the draft link, which allowed her to see it but not to edit it. Then to get around this, I made her a Contributor to my Substack account, which allowed her to see (and presumably edit) everything!
The Contributor designation didn't allow Tracy to see or alter the Settings in my account, I think. And I trust her to edit and alter only the posts on my site where she will be designated as a co-author. But even so, this seems like a pretty broad brush, doesn't it? Wouldn't it be better for collaboration, if Substackers could designate a section or a folder where the collaboration happens and wall off the rest of their sites? I can imagine a lot of situations where creating a "Sandbox" with different privileges could encourage collabs. But I think some people are going to be put off by granting Contributors access to everything. Something to think about, Substack team?
You could do a shared Obsidian vault on Dropbox, to write and edit your posts, then once you've agreed they are ready, post articles to Substack. (Maybe even use the current OBC vault.)