For East Somerville, the emergency egress is at the north end of the platform. That could easily be the site for a direct entrance to Washington Street, as was originally planned. Gilman Square lacks a direct entrance to Medford Street (again, the original and sensible plan), but it would not be difficult to add later. I could also see second entrances at Union Square (footbridge to both sides of the tracks from the east end), Magoun Square (to Murdock Street, where the emergency exit is), and Ball Square (to the north side of the tracks) being viable and relatively inexpensive add-ons later to shorten the walk from nearby neighborhoods.
BTW, the most recent station designs (November 2019) are
here. Not all are 100% design, but I doubt there's been any substantial changes.