> both particles have a superposition of k and ~k (to use your terminology). ... This "internal state" simply does not exist until the wavefunction collapse has occurred.
What would the implications be if particles did have an internal state?
It would be a violation of Bell's theorem as we currently understand it. In other words, it can't happen, unless our understanding is wrong. (For more info, the wiki on Bell's theorem has been linked to elsewhere in this thread.)
What would the implications be if particles did have an internal state?