The glass has to provide good insulation then. Also, I don't know for Boston, but in Quebec if there's nothing to stop mosquitoes it's essentially unusable...
This will not be easy to retrofit.
Studs are not typically designed to handle cantilever loads.
You would pull the stud right out of the wall. You'll at the very least need new (stiffer) studs. By the time you are done with the internal reconstructions (and if it's a load bearing wall, good luck), this will be very expensive.
An ordinary deck is far far cheaper. This is cool, but not practical.
Just lock it, and when the good weather comes, open it. Plus it seems that it will be easy to retrofit to existing apt. buildings.
If it is cheap enough, why not.