Admin note: Moved to Setting Discussion since this is not a Setting Submission (setting submissions require wiki articles).
Maybe, if there is interest. What would be the difference between doing that and just posting them as one-person RP threads on the forums?
The layout of fictionpress.com is more conducive to stories, more so than a forum. If the story is multi-chapter, then one wouldn't have to create a new thread for each chapter he made. Doing so, or alternatively, putting all chapters as posts in a single thread, would create a lot of unorganized clutter, in my opinion.
Second, fictionpress works by you creating a Word document, and then submitting it to the site. The Word document will be added to the story of your choice as a chapter. Chapters, in most cases, require several days of work to complete. Attempting to type a 5,000+ word chapter in these reply boxes down here would be a pain, and may result in accidental deletions or submissions of work. Being able to save whenever you wish, close your work, and return at your leisure is a much better alternative.
A topic could be created which would provide a link to the community, but personally I feel more comfortable using fictionpress rather than a forum to create big literary works such as a book.
A link, to show you what I mean:
https://www.fictionpress.com/
Everything on the site is %100 free to use. All one would have to do is create an account. I would recommend looking at the communities too, where authors can submit stories that share general traits, such as being about romance, or zombies, or what ever.