I don’t think having to get off at CBR and get back on the DHS line would put you at any disadvantage. We don’t know how the CBR station is laid out internally, of course, but imagining from the way Disney handles everything else, there’s probably a “merge point” where people coming from Pop, from Epcot (probably not many at park open, pre-Riviera), and entering at CBR all become equal. CBR guests wouldn’t have higher priority.
I know we don’t “know” yet but I can’t imagine them making Pop people “exit” the station and enter again where CBR guests enter. Probably signs when you get off pointing DHS one way, Epcot another, and finally “Exit to Caribbean Beach Resort.”