While the link you gave seems to not be working, it's also listed as a rumored role on his IMDB page.

I can't say Blofeld's return is particularly surprising. As Quantum seems to be taking the same role that SPECTRE held in earlier movies, this can hardly be considered shocking news that Blofeld might emerge as its leader. At the same time, I had thought perhaps that they might introduce a new character as the lead. Then again, as a reimagining of the series, that's probably also unnecessary.

As far as casting Michael Sheen for the role... well, given that the new series depicts a Bond much more similar to the one we see in the books, we might also see a very different kind of Blofeld. Flemming's description of Blofeld said he was formerly a body-builder who had long since gone out of shape--nothing like his depiction in the previous movies. There's a lot of room for a lot of changes, so I'm not going to worry about casting Michael Sheen (someone who certainly seems odd for the Blofeld role as it's already been established) quite yet.