I think you need to include speculators in your equation. If S is the number of bitcoins being horded, we would get (M - S)V = PQ. Since the perception seems to

I think you need to include speculators in your equation. If S is the number of bitcoins being horded, we would get (M - S)V = PQ. Since the perception seems to be shifting where more and more people believe that Q is going to continue to increase, S becomes larger (and in extreme cases, a bubble).