Partial closures on summer weekends I think will work fine. I don't think a permanent closure would be beneficial or possible.
You've got private parking garages on both ends, plus a surface lot that are all going to (obviously) have a problem with no longer being able to be accessed.
Closing the Hynes end causes issues for access to the Pike ramp and is going to push more people towards Storrow (usually the opposite of what people here want to see) or just going to gridlock Mass Ave even harder with Comm Ave -> Left on Mass Ave -> Right into the Pike.
You seem to be exaggerating the plan only so you can point out the flaws in an exaggerated plan. Nobody's saying that every square inch currently labeled "Newbury" has to be blocked.
At DTX very little is fully blocked. "Closed" ends up meaning "no parking" and "no through traffic" and "rare vehicle drives with full deference to pedestrians"
Here is a reasonable set of rules which are, at least, not strawmen designed to fail and might achieve most of what's being looked for
1) Not applied to cross-streets and applied on Newbury only *between*
- Exeter-Fairfield
- Fairfield-Gloucester
- Gloucester-Hereford,
but doing so also lightens traffic on Arlington-Exeter and Hereford-Mass Ave. The lot at Dartmouth@Newbury would have full access and so would the garage between Hereford and Mass Ave. (Danker & Donohue)
2) Eliminate all parking and standing/idlin, just like an airport curb.
3) Narrow asphalt from 4 lanes to 3 and give a half lane to each side's sidewalk
4) Narrow asphalt from 3 lanes to 2 and give a half lane to a bike lane on each side
5) Use texture / mountable curb for fire/emergency/construction access.
6) Retain 1 travel lane for Taxi/HOV/delivery only. Ensure that every vehicle always has a driver who can move it on a moment's notice or is a real UPS/Fedex/delivery-type delivery, or somebody loading a rug into their car. Enforce with cameras
7) Retain 1 curb lane for ACTIVE loading/unloading only and a small taxi stand, just like the curbs at Logan.