a.js

function A(props) {
  return (
    const {unknown, ...rest} = props
    <A prop={unknown}
      // input still contains a lot of `Unknown`
      // because B require them
      <input {...rest} /> 
      <B {...rest} />
    </A>
  )	
}

A.defaultProps = {
  unknown: 'unknown',
  oneMoreUnknown: 'oneMoreUnknown',
  anotherUnknown: 'anotherUnknown',
  thirdUnknown: 'thirdUnknown',
  onChange: function() {}	
}