Thought I’d throw this in the mix as well— Readwise will import your Hypothes.is notations. I’ve started using Readwise pretty heavily for importing tweets, and realized the other day that it can do hypothesis as well! Readwise has a pretty robust manual export as well as an API.
Another thought, for those who were concerned about privacy… they don’t have a detailed guide, afaict, but you could probably (definitely?) host your own instance of hypothesis! Everything they produce is open-source. The “h” repo is the server code.