Tony, congratulations and welcome to the hot seat! I am grateful you started with the most important thing - i.e. listening. A lot has already been said here but to summarize some of it and more:

1) Writers like me come to Medium because it provides a "freedom" of speech and expression without the additional effort and pain of a traditional blog. Support that with the means you have - bring back mobile editing as taking that away was a regressive step in a world that's shifting from laptops to mobile in all ways.

2) Enhance your supply i.e. fix the platform for writers, and you'll have done a favor to the readers as content will bloom as a result.

3) Disincentivize meta and "how to make money on Medium" type stories - too much of that drivel drives the readers away.

4) Tweak the algorithm so that it levels the playing field for reputations and other factors, and simply promotes the best content and let it be an iterative process that learns from the audience -they're the best judge.

5) Promote discussion beyond "responses" - let writers talk to each other? A chat widget couldn't be too hard to add on? With some strict filters to avoid this becoming another predatory place.

Most importantly don't forget to continually evolve or extinction will continue to threaten this platform like any other. If behemoths like FB can die a slow death, Medium's mortal too.