Regarding the Armory Branch:
Gas Pipeline-
This was called "the Jet Line" and was built during the early to mid 1960s so it was during the New Haven Railroad era. The pipeline followed the Air Line from New Haven to Middletown, then the Valley from Middletown to Hartford. I believe it parallels the main line Hartford to East Hartford, then the Armory from there to Springfield. It continued beyond the Armory branch to Westover Field, the Air Force Base. Its primary mission was to supply jet fuel to the USAF. My Dad worked in Willimansett MA next to where the Westover Branch connected with their Conn River main line and before the pipeline there were usually tank cars stored in the area.
Regarding the "Through Freight Route" concept-
"Engineer Spike" was (and is) correct that the line has a lot of light rail - I believe 78 and 80 lb per yard and even some ex CNE 79 lb rail according to A J Belliveau of the Central New England RR, the operator that has the rights to the state of CT owned line north of the East Windsor Hill area to the State Line in Hazardville, where the track ends. A J did try to purchase some of the line intact north of the state line but did not receive any cooperation from any party, including the former owner, the state of Mass, or even the scrappy hired to lift the track. This remains a sore point with him to this day. As finanaces and time permits A J is improving the existing line, some of it having been out of service since the mid 1970s. I remember one especially large tree that grew in the gauge by a crossing between Hazardville and Melrose that literrly kinked the out of service rail before A J rebuilt the crossing!
Additionally, years ago I asked the question of using the route for through freights - and there were several each way back at the time - to Hartford trainmaster the late Joseph F Daly, who had been at that position through the NH, PC CR (for a short time) and Amtrak. Joe said the PC had studied this but the major problem was a large number of grade crossings (he said around a hundred but that must have included everything down to inactive farm crossings). Many more crossings than the main line, Hartford to Springfield. Add to that the problem of the light rail, mostly cinder ballast and a few surprisingly sharp (but short) grades and possibly some bridges as well.