Blofeld
I know that Christoph Waltz is uncertain about playing Blofeld again, but if Lea Sedoux is coming, he should be back as well and Fukunaga has even toyed with the idea of bringing him back, I know Waltz wasn't a great Blofeld but I think he might have a part in the Craig Bond finale, maybe he might give Bond information about Malek's villain, or breaks out of prison to attempt to seek revenge on Bond and MI6, or something. Have no clue why Craig's Bond has a personal stake in the films though.