Amtrak does not serve the T. F. Green Airport station. They claim there isn't ridership and refused to provide funding, so the MBTA-funded platform is on a non-electrified side track not used by Amtrak.
But, what if the ridership is there? It certainly justifies the stops at BWI in Maryland and Newark Liberty in New Jersey. I imagine that within ten years it'll be enough to justify stopping some Regionals there.
They left plenty of space for an Amtrak platform. There's about 25 feet between the side track and the main 2-track Northeast Corridor, and at least 10 feet between the Corridor and the side of the garage. The Corridor is also about 2 feet higher than the side track.
I pictured a mini-high platform next to the MBTA track (matching the current platform) connected via ramp and steps to a full-high Amtrak platform serving the southbound track, plus a full-high platform on the northbound track.
This view is looking north; the bridge to connect the platforms would either be on the north side of the garage, or further south, on the open-air part of the platforms. I made no bridge here.
The result of three hours in GIMP:
The Boston Projection
1 day ago