The dome was added to the Carbondale service to help meet a recently-imposed operational requirement from host CN. CN is requiring that Amtrak run minimum seven car trains in order to permit full track speed operation. The claim is that grade crossing detection has not been reliable with shorter trains at maximum track speed (79mph). Amtrak is scrounging any and all available equipment to meet that requirement, including use of the dome. I do not know if the dome is open or just along for the ride.
This CN requirement is also being claimed as a reason for the shortened long distance train consists. Amtrak has diverted some long distance Superliners to the other Carbondale train in order to meet the seven car requirement. This included adding two Superliner sleepers to at least one recent consist (not open). Note that the only Superliner long distance train that was not shortened was the City of New Orleans. It operates on CN and must also meet the seven-car minimum length.
Now, the obvious question is why is only CN's detection an issue with short consists? I have no answer. Is it possible that CN is playing hardball with Amtrak as a result of Amtrak's STB filing against them? I can't say for sure, but the dots do sort of connect.