A few author friends and I have been using a "collaborative branching fiction" site I wrote 25 years ago. Took it out of mothballs when Covid hit, spruced it up in some ways. Now it has a react component that graphs the DAG of the stories (threads can merge together, loops are not allowed), lets you filter by un-concluded threads with some nice animation. I wrote some software that will project how big the story will be based off of average chapter length and choices per chapter. I'm also trying to make the site "guide" the authors in terms of how many choices to add, to keep the overall size of the story within certain guidelines. Since we're mostly third-person past-tense, we're trying to maintain a somewhat literary focus so that all threads have pleasing narratives that eventually end.
Our most active story, Story of a Stone, currently has 318 chapters, 1,064 pages, and a total word count of 265,964, or about the size of Ulysses by James Joyce. It has 4 unwritten choices, and a sprawl of 1.35 choices per non-concluding chapter.