The small startups where I have worked have had woefully bad documentation. Developers and support reps never have time or want to write it. I would say the most useful thing I have done for these companies has been to set them up with a basic Zendesk account and just start writing articles to answer the most basic support issues and how-to guides.
I have found these topics to be not very prone to political word-smithing. People are just grateful for the documentation to be written. The company word smiths and bullst artists would rather fight over the copy for the front page of the website than type up "Troubleshooting CentOS Client Installation". It's uncontroversial stuff.
You would have to offer a turnkey solution (set up a Zendesk or Confluence knowledge base for them, perhaps as a value-added reseller), propose a list of articles to be written, then knock it out in a couple weeks, with add-on work to keep the documents fresh with future releases.
Your sweet spot would be companies with 25 employees or fewer who don't have the money to bring in a full time technical writer.
I don't think you could make F-U money, but you could do much of it remotely, and it would be less stressful than other types of work. Your clientele would have to come largely based on personal reference.
Curious if others think this is viable...