Dunno. They're hard up for storage since "Yard 8" on the west side of the Innerbilt got mowed down to just one track (the distended loop-around BET from the Lowell Line) for carving out the GLX mainline. They're probably going to need the Yard 21 stubs for awhile. "Yard 8" was tiny; fixing the collapsing retaining wall so they can use all the space out to Assembly gives them more or less equivalent space (but less flexible switching between tracks). Everything's a TBD because they gave up their title to pretty much all yard claims in Somerville when they sold all their land for GLX. The tracks by Sullivan are less convenient to work around than what they had before, but they have no leverage anymore so they're just getting shoved in the nook/cranny that keeps them furthest out of the T's way.
Now, if you're thinking "What happens if the Urban Ring needs those tracks?"...there are the easy-reach offsets that get them out of town:
- Carve out more yard space inside Everett Terminal by the gas tanks (ditto if the 2 storage tracks along the Eastern Route between Sweetser Circle and 2nd Ave. need to be taken for UR). Generous amount of space there. Would just need some quid pro quos with the private Terminal owners.
- Rehabilitate Montvale Yard (T-owned). PAR uses the two tracks next to Tighe Warehouse in the Winchester Industrial Park for setoffs on the nightly overnight Winchester local to Tighe. There's another disused 1000 ft. x 2-3 tracks of yard space buried in the thick overgrowth running north of that warehouse in the Draper St. backlots, to about the edge of the cemetery. If PAR could be coaxed with carrot+stick to run on-time (which they rarely do) this is a midpoint pull-out where they can stage the Everett and Peabody jobs, getting them out of Somerville except on pauses between commuter slots.
- Rehabilitate Winchester Running Track. Just south of Montvale there's a long third track siding on the Lowell Line, occasionally used to store T work equipment overflow. About 1400 ft., but cut off at its north end. If they reconnect the Cross St. end it'll double in length and act as a parking spot for staying out of the T's way. Or, they can lengthen to Cross St., replace the (kinda decrepit) Cross St. bridge with a tri-tracker, and extend that lead into Montvale Yard to give them about a mile's worth of layover track and the un-buried Montvale Yard tracks together for staging themselves on either side of Boston.
I'm guessing any of those or preferably all of the above would permanently satisfy all their needs, and let them triage their loads on either side of the Mystic so Somerville can just be a pausing spot. All are cheapies, and as mentioned PAR has bupkis for leverage after signing its life away so they'll play along wherever the MassDOT freight fun bux tell them to go. Of course if/when PAR gets bought out by somebody who gives half a shit about running on-schedule they won't have to can nearly as many loads overnight near Somerville to begin with because they'll get back to base out in 495-land in one shift. PAR doesn't truly need much space at all in Boston, except in terms of their infamous brand of "slop ops" that can't stay out of their own way.