I think ND needs a 'personality' to get over the top. BK's 'business' approach has gotten the program back to a great place, and if he hits on a QB, it will be enough to finally win a natty, which is about all you can ask for. But if you can find a guy that can maintain/steward that foundation, while also offering a little something more in terms of the motivational aspect that can bleed into both recruiting and game prep, I think you'd have what you need to win a natty for sure.
I used to think that guy would be Fleck, but it seems that maybe he's just a one-trick pony. But I DO think you need a guy that isn't afraid to go beyond "we're gonna play for each other and play hard for four quarters and play like champions today." You need someone that's gonna get the locker room shaking, talking about waking up the echoes before a home game against Clemson, or a guy that's going to summon the ghosts of the Four Horseman before a game against Ohio State.
That guy is gonna have the players ready to ride the emotional rollercoaster when necessary, and he's also gonna be able to parlay that into recruiting.
Though I will admit that it is an extremely fine line that the next HC will be toeing, because the current recruiting ideology is obviously in a better place than it has been since BK arrived (and probably in a better place than Charlie Weis had it; despite CW's top-end recruiting, depth and developmental projections suffered badly almost every class). We've seen more hits, more depth, less total misses, etc. in the past few classes, which has resulted in a roster with few holes. Even when we see doom spelled out because of injuries and bad luck at a position group, BK's got the program in a place where they can mask it for a year by leaning on a different part of the roster.
But if the next guy comes in and tries to use his personality to go over-the-top, it would be really easy to fall back into the '11/'12 trend where you sign a bunch of great players with big personalities that don't necessarily mesh with the current foundation, and it becomes subtraction by addition.