I believe the Custom House Clocktower only got built because it was a Federal building, exempt from the local rules. That was all the way back in 1915. I consider that and the Hancock to be the 2 most iconic buildings on the skyline by far. Will we ever see such a bold statement like either of those buildings ever again?
This one looks fantastic, but is in that next tier with The Pru (love it or hate it, I love it), 1 Dalton, Millennium Tower, upcoming State Street Tower, and The Fed. Given that it's about the exact same height as 5 other existing buildings downtown, it's tough to go so far as to say it's the "Hancock" of the waterfront. If anything it will share the spotlight with International Place and the Custom House. The only way we are going to get another "Hancock" impact building in this day and age is to actually build something as tall, or taller, than the Hancock itself.