Two World Trade Center, one of the final pieces of the ground-zero rebuild, is finally happening. We've seen plan after plan for it since the aughts, from Norman Foster and Bjarke Ingels and then Foster again, and the latest iteration of his latest one, first shown several years ago, now has a tenant and a completion date. American Express announced this morning that it will move out of its longtime home at 200 Vesey Street, just across West Street, and take the whole building, all 2 million square feet of it.