Firstly, Expo is amazing! And I know you’re all very busy and giving away work for free-- so this is just meant as constructive feedback, not bitching and moaning.
That said, from expos perspective, it might make sense to push up in-app purchases on the road map. 85%+ of apps will need to monetize somehow. Right now you have ads covered with facebook Ads but the other major business model is of course in app purchases. With in app purchases, you would have 85% of use cases solved (from the business side of app building not the technical side). In some ways, you could argue monetization features should come before technical features, as in many cases monetization is the #1 reason behind building an app in the first place.
In summary, I think there would be a huge return-on-time-investment for Expo to add in app purchases. Otherwise a huge number of app projects have to (1) start an expo app knowing they’ll need to eventually eject anyway, or (2) begin with another non-expo option. Probably way more apps need in app purchase functionality than apps that need, say, a document picker (which is an awesome feature no doubt!). So, just my two cents.