That is the key decision that Shopify, Substack, Teachable, Superpeer, MyVillage, Wonderschool, WeeCare, Squire, Dumpling, SmartHop, and every other BiaB platform will ultimately face.
But becoming an Aggregator can also lead you astray from your core focus and vision, and can upset the businesses that came to your platform to launch in the first place, precisely because they did not want to get aggregated down the road. The most successful businesses created on the BiaB platform could leave.
Platforms facilitate a relationship between users and third-party developers. Aggregators, on the other hand, intermediate the relationship between users and third-party developers.
Substack could decide, for example, to provide an app that showcases all of its writers, enabling a user to search through the newsletters, browse articles, and sign up for those they wish to. This would be analogous to the Shop app by Shopify.