I think being completely in control of what shows up on your dashboard is definitely important, I'm not sure how fine grained the controls could be made. All the way to the algorithm?

Another one I think is being able to control your data. Who sees it, which part of it, and so on. Being able to delete data you don't want to keep, etc.

One of the advantages of paid accounts is that it's quite pricy to pull off a lot of shady things that are currently prevalent, spreading fake news for example.