> Actually, I linked to a proposal by Brendan Eich, the creator of JavaScript.

Naming names doesn't change the idea: It is surely a wholesale change to function semantics in the language.

> JavaScript's open prototypes suffer from the inability to define a number of new properties at once using an object literal. reopen (not reopenClass), provides that functionality.

Sure, that's why you use a general-purpose merge function, prototypes just being objects themselves.

  var merge = function(o, o2, force) {
      for (var p in o2)
          if (o2.hasOwnProperty(p) && (!(p in o) || force))
              o[p] = o2[p];
      return o;
  };

  var C = function() { /* ... */ };  
  merge(C.prototype, {
      foo: function() { /* ... */ },
      bar: function() { /* ... */ }
  });

In any case a name like reopenClass() sounds very much like an attempt to make JS smell like Ruby even if all the function does is perform a merge.