I don´t think they would do it, having Waltz in the ensemble.
Then again, if the character were re-booted as a woman - Monica Belucci would be the most attractive Blofeld yet.
But really, I don´t think EON would go for that. They know that the press would jump on it, comparing Barbara Broccoli with a female Blofeld etc.
Nah, it will either be Waltz or...
... someone else completely who, of course, has not been revealed yet.
Because that would be the real surprise. And why would they want to come out with that during the first photocall?
I don't think they go that direction, either. That said, my reaction would be similar to the one I had while watching The World is Not Enough when Electra was revealed, which was that of indifference.
I think if Blofeld is actually in this film, then it has to be Waltz. If they hired him to be a red herring and cover for someone else being Blofeld, then I hope they compensated him well for the grief he's going to have to hear from the press for the next 11 months, with every interview beginning with "So, you're playing Blofeld, right?"