Expanding further on my other post here.
The RUS feasibility report for the Greater Triangle Commuter Rail (GTCR) project included some details about new platform construction at RUS. While three alternatives were proposed, NCDOT preferred only two of them, and one has a (significant?) cost advantage, leading me to believe it is the current preferred solution. This could change, of course, but I feel that it is the most likely at the moment.
Essentially, a portion of the north platform for future S-Line trains will be constructed, and all Piedmont trains will be directed to that platform. A tunnel will connect the platform to the station building. Then, commuter trains + intercity trains (Carolinian and Silver Star) will stop at the current platform. Also note that this solution would impose some constraints on the commuter rail rolling stock, as it would require high-floor trains to service the 48" platform at RUS, i.e, no bi-level coaches.
Here’s a diagram:
