Sass, I know that there are beta pubs ( the writing cooperative, stories, etc.) that are going to offer a paid membership that unlocks content your average reader won’t be able to see. For The Writing Cooperative the cost ( for now) is $2/month. The idea is to charge the readers. However, those of us who write are Medium readers. So yes, writers who also read would be paying, if they so chose, to read certain content. Also, readers who don’t write will be given that same opportunity.
At this point in time, I have not heard anything about paying to WRITE content. Work will still be submitted as it is now, but those whose work is chosen for the paid content will start to receive some compensation. The ability to write and submit anywhere is not what is being monetized.
That’s how I understand it.