My biggest gripe with Substack is subscriptions. There are many creators and there are many worthy articles written by them. But, you might not be interested in all articles written by an author. And, subscribing to all you are interested in quickly adds up.
I would rather have a credits system (like audible), where you have a monthly subscription to Substack and you use credits to buy access to articles you are interested in. Or something similar.
I'd love to see a "tip" feature implemented as well. A credits system is interesting though.