If they redesign it (MBP) enough, they may use it as justification to bump up the base price of it up accordingly. In which case, I doubt you will get one for $1700.
There is also the possibility that if for whatever reason, the base price of the MBP remains steady, and there is redesign to make it thinner, they may drop the price of the rMB slightly when the MBP is released.
A lot of "if's", admittedly, but there's just as much chance of any one of them happening as there is that the prices will remain exactly as they are now.
Economies of scale factors into all of it too, which will also contribute to the likelihood of a rMB price drop, but personally I don't think we'll see that until 2017. I suspect Apple will raise the base price of a redesigned rMBP, and there will be an outcry here in these forums, but people will still buy it.