I suppose given that McClory is dead that might now be a possibility. I always liked Telly Savalas best as Blofeld, but to be fair there really isn't much to compare him to as the other times he functions more as a caricature or stereotype rather than an actual threat.

Given the more realistic nature of the Craig films I'm going to guess SPECTRE isn't in the plans for now... oh well, one can hope we get serious villains nonetheless. I rather liked Javier Bardem's character in Skyfall and think we have a chance of getting compelling villains like him without the personal connections that tied him down (re: M revenge plot.)