...if you want the franchise to be about Batman.
Why is it that the Batman movies always end up focusing on the development of the villains, no matter who's directing the franchise? People find evil more fascinating than good, the villain/anti-hero more intriguing than the hero, at least in our culture people see good as static, unchanging, you know, "Happy families are all alike; every unhappy family is unhappy in its own way." However I believe that one series, Naruto, has shown that to not necessarily be true. Also, the villain in each movie is a new character whose development is unknown. Basically there is stuff going on in the character's life that is plot worthy. Changes in his or her perspective, choices to be made, etc. The Batman problem is that once you move beyond the early years of Batman's career, there's something of a... plateau in his character. While he does face new enemies and new situations, once Batman/Bruce Wayne has figured out how he wants to be Batman, he's in a rut until something comes to shake him up.
The most obvious way to shake up Batman's life is to introduce a new love interest, preferably one that has dubious morals. Many writers have this done excellently with characters such as Catwoman, Andrea Beaumont, and Talia al Ghul (Whom I greatly dislike, but that's another post entirely. Let it suffice to say that her character serves its purpose.). However, Batman has mastered the art of love 'em and leave 'em (not to say that he hasn't been left as well). The problem here is that romantic dalliances are too easy to get rid of. Be an ass, get absorbed in "work", forget a few birthdays and monthly anniversaries, disappear in the middle of every other date, and basically be emotionally unavailable. It does hurt if Batman actually likes the person, but it's not hard to do, especially when he has a subconscious belief that he might not really deserve love working against him.
The one life-shaking commitment that Batman hasn't been able to get rid of are his relationships with his sons, and I believe that an objective read through of the comics and the cartoons will show that Dick Grayson is the person who remade Batman into Bruce Wayne. Before bring Dick into his home, Bruce could disappear into the cowl, and there's nothing that anyone--even Alfred--could do about it. Bruce's reasoning seems to be that with both romantic assignations and parental relationships, the people involved are adults; they got into a relationship knowing who he is and what he's after, so whatever pain they feel at his choices, while regrettable, is their choice to experience. They walked in and they can walk right out. The same cannot be said for the young boy that Bruce first gave shelter to, and the love and responsibility that he feels for Dick turns his internal world upside down. There's nothing that any writer has added to the Batman mythos that's been as effective at throwing Batman out of his character rut as introducing Robin. It pains me that a certain director is so set against including Robin because it's "unrealistic" (as if a man dressing up as a bat and revolutionizing crime and law enforcement in crooked metropolis because his parents were killed in front of him at nine years old is realistic).
That is not to say that I don't appreciate Mr. Nolan's vision; his Batman movies has completely revitalized the franchise and I love that he takes the story seriously, treats it like what it is-a story-and make the best story possible. If anyone can shake Batman up without Robin, it is Mr. Nolan, but--call me a doubter--I just don't think that's possible. And I do believe that that's why he is focusing on the beginning of Batman's career before he reaches that plateau that requires a Robin, when the shaping of Batman's identity is still very much in flux. I believe however that it may leave the franchise... incomplete and I worry that the next director of the franchise will not approach the franchise with the same skill or gravity. I am looking forward to the Dark Knight Rises (in my mind I call it Inception 2), so really it's nothing more than a waiting game since Mr. Nolan's tenure is almost up.