useImperativeHandle have bug in 16.8.1 if you want to access any state will get the initial state not current state but in 16.8.0-alpha.1 it work good 

You can see here https://codesandbox.io/s/xjl8znwpz open console when you change input value will get the currently value in console but if you clicked button get value from ref will get initial value (e)

If you try same here https://codesandbox.io/s/qxkll6po0j with 16.8.0-alpha.1 when clicked button get currently value

create: () => (() => void) | void,
      deps: Array<mixed> | void | null,
    ): void {
      currentHookNameInDev = 'useLayoutEffect';
      return mountLayoutEffect(create, deps);
    },
    useMemo<T>(create: () => T, deps: Array<mixed> | void | null): T {
      currentHookNameInDev = 'useMemo';
      const prevDispatcher = ReactCurrentDispatcher.current;
      ReactCurrentDispatcher.current = InvalidNestedHooksDispatcherOnMountInDEV;
      try {
        return mountMemo(create, deps);
      } finally {
        ReactCurrentDispatcher.current = prevDispatcher;
      }
    },
    useReducer<S, I, A>(
      reducer: (S, A) => S,
      initialArg: I,
      init?: I => S,
    ): [S, Dispatch<A>] {
      currentHookNameInDev = 'useReducer';
      const prevDispatcher = ReactCurrentDispatcher.current;
      ReactCurrentDispatcher.current = InvalidNestedHooksDispatcherOnMountInDEV;
      try {
        return mountReducer(reducer, initialArg, init);
      } finally {
        ReactCurrentDispatcher.current = prevDispatcher;
      }
    },