Not privacy-focused, but OKCupid itself fit many of your requirements when it first came out. It wasn't aggressively seeking hyper growth and barely marketed outside of existing SparkNotes and SparkMatch users. It was just a few math nerds at Harvard that wanted to model human romantic compatibility by categorizing you into a shareable cutely named personality type, and they bolted on crowd-sourced questions to see if whatever they hadn't thought of themselves might be relevant.

Ten years later, the social media revolution is in full swing, the relatively small service they built that had catered mostly to nerds was suddenly lucrative, and they sell to Match Group and this happens.

To be entirely fair to these guys, I don't think they came into it intending to sell out as their long-term goal. But four guys who got into data analytics in college also didn't find themselves as their mid-30s approached particularly wanting to run a dating service for the rest of their lives, either.

Whatever happened to FetLife? If any dating service had to be privacy-focused, that was it.