First of all, it needs to be a good building. Not like the junk recently built in Edmonton or being built in Austin. The design and execution need to be spectacular. It shouldn't be glass dominant either, as we already have 2 major towers like that now and it's kind of the Hancock's "thing." Also, a supertall is technically at least 300m, or 984', which likely isn't feasible anywhere in Boston. However, I would like to see something certainly over 800', if not 900', right on this particular parcel. Here and the Kings parking garage seem to be the only real places that could do it. North Station area could maybe hit right around 800' on one of those parcels, and Kendall could certainly do it but they haven't really figured that out yet. But for 900'+ in Boston it's this area of Back Bay or bust, and the FAA map has a very limited amount of parcels where it could work.
Not only do I want to see the height that is deserved, I just as much dread to see something shorter with the kind of view-killing width that will permanently wreck the (still) graceful look of the Back Bay skyline. I'm terrified of that fat undulating garbage building at the Back Bay Garage site blocking off a few too many views of the Hancock, and would hate to see that spread toward the other 2 Back Bay giants. It's an aesthetic thing, and not just from "the suburbs" or far off views. These giant walls and uninspired stumps often block off many better views within the city itself. They detract from the feel. For example, 888 Huntington took away the absolute top view of the Pru and 111 Huntington from across Boylston, and actually makes the city there feel smaller by its presence. Young adults today will never know the experience of stumbling out of a bar to the awe inspiring view of those 2 buildings towering over you.
So really, this parcel feels like it's it. It's the main shot for me to see a new tallest building before I die. Sure it doesn't solve all the cities other problems, or cure cancer, or promote world peace, but so what? When the Red Sox won in 2004, it didn't do any of those things either, but people cared. I care about this, and while it may not be the 2004 Red Sox groundswell, a lot of other people care about it too. (just, ya know, less than the archboston poster with the proverbial bullhorn)