I thought the same thing. Nothing a little JavaScript can't fix:

  // Insert drop down item.
  var li = document.createElement('li');
  li.innerHTML = '<a href="#">1000wpm</a>';
  li.setAttribute('data-value', '1000');
  document.querySelector('.speed ul').appendChild(li);
  
  // Create 1000wpm script
  var s = document.createElement('script');
  s.id = 'learntospritz_en_1000';
  s.type='spritztext';
  var data = JSON.parse(document.querySelector('#learntospritz_en_500').innerText);
  data[17] = '1000';
  s.innerText = JSON.stringify(data);
  document.body.appendChild(s);