I'm talking to myself at this point, but I think the problem with the caching is that every attribute lookup p.x has to consult the type, not just the object.

I'm talking to myself at this point, but I think the problem with the caching is that every attribute lookup p.x has to consult the type, not just the object. That's not true in Java. So you avoid the dictionary lookup, but you're still following extra pointers.