React Native is missing touch sounds/vibrations.
This is the only thing that gives away that the app is not made natively.
Take a look at the instagram app for example, there's no sound. This gives you a clue which components are native and which are React Native.
Adding this feature will make apps feel more consistent with other native components and almost impossible to tell if it's a react native app.
There have been PR attempt in the past but unfortunately it wasn't successful.
A subtle little feature that will go a long way!