They didn't add the originally planned cladding because the spire would vibrate and might even damage itself with the powerful winds. This was proven in the wind tunnel tests.
This great documentary by PBS, at 37:14 to 38:25, explains it.
I agree about its beauty with the cladding, and yet, as shown in your pictures, that part of the spire it's having a different kind of cladding. And as I wrote, "I hope it turns out well".