opting into Hermes with React Native
Hermes is an open-source JavaScript engine optimized for running React Native apps on Android. For many apps, enabling Hermes will result in improved start-up time, decreased memory usage, and smaller app size. At this time Hermes is an opt-in React Native feature - Hermes
Open Questions
Hermes vs React Native's defaults: What is the impact?
Apparently no blockers to using Hermes today. Intl and Proxy polyfills work fine 1, 2