Got a call from the hotel (or better said the Hilton Berlin) a few days after my e-mail. Had a very nice chat with the guy.
The hotel will not be open before January 1st 2013. They are still working on the rooms and the interior.
He offered me to cancel the booking or to change the booking to the Hilton Berlin. Offered me a good rate for the same room category, which was a Corner Suite (same as great getaway + flexible cancellation until 4pm + free breakfast + special VIP treatment). Took the offer for the Hilton - first time there, but I think at least the view will be great...
And he offered me also a guaranteed upgrade at the Waldorf the the next category of rooms / suites for my next booking.
So all in all I am quite happy with the interaction with the Hilton / Waldorf staff and look forward to the stay at the Hilton - and my first stay at the Waldorf sometime next year...