That question has been posed a few times, and I don't think anyone has ever gotten a concrete answer. One thing is certain, the current Target Field Station isn't going away. I do think that the two platforms (the existing and the Interchange) will be considered a single station. Before and after Twins games, I believe they will use one platform for Green Line and one station for Blue Line.Thanks for the rendering! I had not seen that... Im assuming the interchange eliminates the stop that is currently infront of the stadium where the line ends now?
On non-game days, common sense would dictate that the trains do not stop at both platforms. Maybe the existing platform will only be used during games, but who knows really. They could opt to have separate platforms for Blue/Green at all times, but I hope not. That would be unnecessary and inconvenient for transfers, due to T.F. having a center platform and Interchange having side platforms, as well as the extra walking (luggage, children, disabled, etc).
IMO the Interchange Station should have been built with side AND center platforms to easily facilitate transfers and handle the increased passenger loads. Trains could open doors on both sides, allowing quicker boarding of heavy loads. The existing platform could probably be eliminated in that scenario.