For me at least Substack presents a solid wall with very little to help discovery. Who do I subscribe to and why? The website is awful at showing me interesting writing. Right now they seem heavily reliant on the writer already having a platform and there is no opportunity for serendipitous discovery.
I've also got the sinking feeling that it won't reduce the proliferation of low quality content for clicks because that business model is perfectly feasible in the subscription world. It might even speed it up as people gravitate towards paying for content that they agree with or tickles them.
I'm also concerned about what this paywalled, atomisation of information and ideas does to society. Looking at the subscription rates it looks very expensive to maintain a rounded view or even to subscribe to more than a handful of writers. If we're going to complain about newspapers and journalism losing their way (in a value to society sense) does the model of Substack actually fix it or is it just a way for a minority of writers to find financial success?