The Sheraton actually did open up retail facing Belvidere - a hair salon day spa kind of place. Looks nice on Belvidere though the street interaction could be greatly improved (See
https://goo.gl/maps/GWKScDLPmaA2). If they wanted to, they could also open their bar area to the outside with outdoor seating on Belivdere (next to what's the day spa) - no idea why they haven't done this, but it would be easy enough - and would greatly benefit the nearly windowless lobby. I have a hard time seeing them ever build out over the porte cochere.
Meanwhile, the CSC colonnade building actually does have a retail spot facing Belvidere too - they were trying to lease it last year. Right now it's functioning as the construction office. (Right here:
https://goo.gl/maps/TQwyUWMbjsP2)
I hear you on the Hilton. I can't think of a single redeeming feature about it. I find the most urbanistically insulting thing is that, on the ground floor of the parking garage, they have a... plastic picnic table streetside. Wtf? Right behind a vent blowing hot air onto the sidewalk. (Here it is:
https://goo.gl/maps/pAXSs2uBCsx) Oh, and their lobby blasts chintzy pop music out of tinny speakers into the driveway.
There are lots of other things about this immediate "neighborhood" that should and will eventually change, though perhaps not in this development cycle. The Kings garage and what I call the Homeless Garden by the Hynes loading ramp, for example. Other eyesores won't be going anywhere like the NStar and Verizon buildings.
I used the word "neighborhood" in quotes before, but I am hopeful that with these changes this corner of the Back Bay - and really, it's quite distinct from the Back Bay that most people think about - will take on a character that's more than the conventioneer-warehouse it is now.