There is definitely a gap for a product like this. At Ritza (a tech writing agency) we use a hacked together set of tools to accomplish this so I definitely see the need and am probably part of the target audience.

Some feedback (based on a quick skim - you've probably thought about all these more than I have but just in case anything is useful)

- Why include project management? It's hard to beat a tool like Linear, Trello, Jira or whatever people are already using.

- I like the idea of a built-in markdown editor, but I think it's also important to allow technical people to bring their own editor or use git directly. Do you support this? If yes, I'd call it out on the landing page. Gitbook used to do this pretty well but they pivoted to a more GUI-focus and now there are weird bugs if you try to use both their editor and git directly

- I agree with other comments that images are something to get right for something like this. Let people paste from clipboard, upload a file from their machine, or link to an already hosted file. Allow the user to the optimization similar to TinyPNG automatically (maybe also CDN, or at least allow integration with CDN). Assuming you're dogfooding this for your own docs, images are loading very slowly so I assume you're not doing this atm.

Good luck!