The Westin/ Marriott ain't going anywhere, or getting taller in our lifetimes.
The Sheraton Towers complex is hideous and dated. The North Tower is the most egregious:
its massing and appearance are a disastrous blight, and has been a millstone on the quality
of High Spine west of the Pru since most of us have been alive.
With it's fair massing, the South Tower doesn't need to go–it just needs to be re-glazed.
Such an upgrade would be a "home run" for the South Tower imo.
The City can inquire with Marriott Hotels about giving these (Sheraton) towers a facelift.
Such a request would be unusual, but hardly unreasonable.
The North Tower would (obviously) benefit greatly from the facelift, but there exists an even better
opportunity to "fix" the Sheraton complex (however incredibly slim) in an significant way....
https://www.google.com/maps/place/S...4bcfbe62b2c7d3!8m2!3d42.3465151!4d-71.0839224
Let's take a look....
It is highly unlikely that circumstances ever make it desirable for Marriott Hotels to remove the North Tower.
Therefore; cut 2 or 3 cells/rows of rooms from the east side of the North Tower (closest to the Pru),
and build a tall tower joining the North and South Towers at the east side of the parcel,
Build it tall; 35, 40, 50 stories up to 600' and beyond, possibly rising in a peak toward the South Tower,
as to greatly reduce the loss of views from 1 Dalton over Back Bay.....