That Mass Coastal has freight rights on an MBTA line that hasn't seen freight activity in 20 years is provocative. A Google Earth exam of the line doesn't even show any potential shippers. The Bay Colony RR NEARS presentation of April 2017 at the link below indicates that BCRR had freight rights on many state-owned Old Colony lines such as the Plymouth Branch from 1980 (start of Staggers Act dereg) until BCRR lost the lease in 2007. So Mass Coastal apparently did not acquire Plymouth Branch freight rights from its recent acquisition of the remains of BCRR.
https://nears.org/presentations/NEARS_S ... Colony.pdf
I don't understand why Mass Coastal advertises the Plymouth line as an "Operating Line" with Braintree interchange on its corporate website given there are no shippers on the line unless something is brewing (eg, a new C&D or municipal waste transload facility). Having said that, given that MBTA trains no longer operate between Kingston and N Plymouth, a couple miles of excellent quality track might be re-purposable if residents are willing.
Strategically, I wonder why CSX doesn't cede its SE Mass freight rights to Mass Coastal and establish interchange at Framingham?