There are a lot of things that can be made to work if one has either infinite resources or a Weimar printing press.
There is no demand in downtown Peabody to support a Blue Line extension. Further, there is no parking. In the words of Gertrude Stein, 'there is no there there.'
True story: the Bev/Salem/danvers/Peabody/Marblehead mini-metro has more people than Worcester, in a slightly smaller geographic footprint
And: its not about blue line TO peabody, its about blue line THROUGH peabody.
Just like there's not a lot of parking in Davis Sq either - and not a whole lot of walk-ons at Alewife ...