But what about integrity of service over time then?
All of this means losing initial flavor of 'doing-things-differently', a lot of other companies can provide boilerplate '-stack' for publishing newsletter (ie, recent yc news -https://github.com/knadh/listmonk - self hosted). So, in the end, the only edge of content hosting platform is how well it delivers it's content (UX, rec systems, internal ads), the bigger substack gets, the less of an edge for its creator base it will have - same as medium.com.
I risk a statement that substack is happening only because medium.com is ending.
Yes, as an author I would be interested in hassle free publishing, but after that, i am interested only in how service is helping me grow an audience, nothing else.