The proposals I saw for the BLX are all a bad joke requiring fantasy bridges across the Saugus River either above or below the General Edwards bridge, either of which would require substantial private land taking. The old ROW is just narrow gauge single track width and building a bridge there...
The only way to fix this problem is for the state to pay the infrastructure bonds. The state mandated the T to take on these projects, the state should pay for them.
The financial problem the MBTA has is fairly unique in the world of mass transit. Pretty much everywhere else major...
The North Shore line crosses the Orange line before it goes underground. If the North Shore Line was four tracked and electrified to Lynn it would be eminently doable and far cheaper to extend the Orange line to Lynn instead of the Blue Line.
Orange line trains could run on the outside tracks...