I don’t know how much is Machine Learning being used to tailor Medium content to the user taste and needs. From my short experience so far I would rate the daily email I get decently relevant, while the recommendations I get on site, in particular on the posts I read, are fairly poor. This could be due to the fact that I am new and hence it will take some time for the AI to learn my tastes. I would definitely be willing to answer more questions to accelerate this process when I have finished reading a piece of content.
The day someone is able to build a system where I don’t have to search anymore for valuable content for me all around the web, I would definitely be willing to pay a decent monthly subscription given how much time it would save me from having to scroll through content that I don’t care about.