On the one hand I like this, as it adds in more shared functionality across both iOS and Android out of the box (maps for example). On the other hand, I believe this also breaks the ability to add in custom RN modules, which is part of the reason I enjoy it. Would love to see some of this getting folded back into react native core.
Exponent maintains native modules so they continue to work when React Native changes or when Android & iOS change their APIs. In particular, React Native is released every two weeks and we stay on top of the changelog so you don't have to regarding native modules. We also write native code for both platforms in tandem, often by the same engineer, so that we get coherent APIs that cover common features across both platforms and expose platform-specific capabilities neatly. We want Exponent to feel like a coherent project. All of the docs (and code) for Exponent's modules are in one place, and when you download the Exponent app for development you get all of the native modules right off the bat.
As a data point, the Android version of Li.st (https://play.google.com/store/apps/details?id=st.li.listapp) is built on Exponent and was featured by Google in the Play Store. Li.st is currently one of the best examples of how far you can go with Exponent, and React Native for that matter. We're also on Slack (get an invite here: https://slack.getexponent.com) if you want to chat in real time.