Thanks for sharing some great ideas that Medium can incorporate. There are so many ways they can improve the system. We also have to consider that they are also a business venture. In terms of the latest financial statement, Medium is still not making a profit (or running at a loss to make the platform accessible first).
'Medium' can incorporate some of the following too:
1. Pay/earnings might be increased based on Reader's choice/preferences (if gets higher views with higher spend time). They might create a matrix, which will increase the pay for the writers). Also, curated articles should get a better form of payment.
2. Top 3 writers in each category can be waived with monthly payment, which can motivate the writers to write more quality content.
3. Tiered membership is a good idea. As there is no way to mark quality comments, but if writers have a way to recommend or mark the readers' feedback secretly, so that every month - top quality content comments reader can get some waiver in the Medium membership fee. It will increase more readership and also better engagement.
There are so many ways to improve the scenario, earning, and also the way to popularize the platform. I hope they will make the necessary changes when time permits. Best regards.