Expo these days is pretty extensible and the option to write your own IAP module is a bit easier with Expo Modules, which let you write custom modules with Kotlin and Swift and set up a config plugin to automate changes to your Android Studio and Xcode projects. It definitely would be good for more IAP modules to provide config plugins and automatically integrate with Expo.

The ability to write and run your own update server is a part of Expo Updates and it is not going to be removed. The Expo Updates protocol is an open specification here: https://docs.expo.dev/technical-specs/expo-updates-1/.

Separately, EAS provides an optional, hosted service that implements the server side of the standard Expo Updates protocol and supports both simple and more advanced deployment patterns, for instance: https://docs.expo.dev/eas-update/deployment-patterns/. It also integrates with EAS's build service and appeals to teams looking for managed cloud infrastructure.