The problem with Nolan is that he'd want to co-produce with his wife and their company, and that would not be welcome. Also, he writes or co-writes all of his films, and that probably wouldn't happen, either. While directors do some rewriting, no director has ever gotten a writing credit on a Bond film.
Wasn't Tyldum heavily rumored before Mendes signed back on? Also, agreed with those who say that Mendes has first dibs on Craig's remaining Bonds.
I half expect and have a bad feeling the producers will offer it to Tom Hooper at some point, because he's won an Oscar and because he's genre-hopped (sports movie to historical biographical drama to Broadway musical adaptation) with enough success to come off as versatile, though he's more of a journeyman director who's good with actors for the most part and picks projects well. Being a journeyman, as it were, can only help his case with EON, as he won't try to rebrand it under his own stylistic umbrella the way a Tarantino or Scorsese might. In other words, he's not the kind of director who has a visionary, distinctive style that would threaten to overtake a Bond picture. Personally, I hope it doesn't come to pass, as I couldn't take his Dutch angles and muted color palette (the few stylistic touches that he has made consistently his own).